Au(III) π‐Allyl Complexes: Synthesis, Structure, Reactivity, and Catalytic Applications

π‐Allyl complexes of transition metals are key species in organometallic chemistry and homogeneous catalysis. Palladium(II) π‐allyl complexes in particular, have gained a lot of attention, but their isoelectronic gold(III) counterparts long remained elusive. However, this situation changed during the last few years. This concept article describes the preparative routes, characterization, structure and reactivity of such species, together with their catalytic applications. The influence of the ancillary ligand at gold, either (P,C)/(N,C)‐cyclometalated or (P,N)‐hemilabile, is analysed in detail. The Au(III) and Pd(II) π‐allyl complexes are also compared to highlight the similarities and differences.


Introduction
Despite the spectacular progress achieved over the past ten years concerning Au(III) complexes featuring carbon-based πligands (alkenes, alkynes, arenes), [1][2][3] Au(III) π-allyl complexes remained elusive until very recently. [4]7] It is only a few years ago that the first Au(III) π-allyl complexes could be isolated.They were reported simultaneously by our group and Tilset's group, using (P,C) and (N,C)cyclometalated ligands, respectively. [8,9]From there on, the chemistry of Au(III) π-allyl complexes was explored systematically and thoroughly, [10][11][12] ranging from fundamental aspects such as their synthesis, characterization and geometric/electronic structure, to their reactivity towards nucleophiles, and finally their catalytic applications (Figure 1).These studies are summarized and analyzed herein, with special emphasis on the role and impact of the ancillary ligand at gold.Particular attention is given to the specific features of the Au(III) π-allyl complexes when compared to their Pd(II) counterparts.
The bonding of the allyl moiety in complexes 3 and 6 turned out to be quite different, and we have chosen to draw the complexes in their most representative form (symmetric η 3 -allyl versus asymmetric σ + π-coordination, as discussed below).
With the first two cyclometalated Au(III) π-allyl complexes being prepared via a redox neutral halide abstraction from the σ-allyl precursors, the question arose if they could be formed via oxidation from Au(I) to Au(III) as is often the case for their isoelectronic Pd(II) π-allyl analogues.In other words, can Au(III) π-allyl complexes be prepared from allyl electrophiles and Au(I), akin to the Pd(0)/Pd(II) elementary step in the Tsuji-Trost reaction?
While Au(I) is infamous for its reluctance to undergo oxidative addition, recent efforts have shown that carefully selecting the ligand allows for the oxidative addition to proceed. [13]In particular, the hemilabile (P,N) type ligand Me-Dalphos has been demonstrated to be very efficient in triggering Au(I)/Au(III) oxidation. [14]13c] With this in mind, allyl acetate was reacted with the in situ formed (P,N)Au-(I) + (Scheme 2). [11]Unlike its Pd(0) analogues, the Au(I) to Au(III) oxidation did not proceed spontaneously and instead, the Au(I) π-alkene complex 7 was formed quantitatively.Despite the enhanced π-backdonating ability of gold induced by bending, the (P,N)Au + fragment was reluctant to undergo oxidation.However, addition of the strong Lewis acid tris(pentafluorophenyl)borane (BCF) resulted instantaneously in abstraction of the acetate.The ensuing Au(III) π-allyl complex 8 is stable up to À 30 °C and was fully characterized using multinuclear NMR.
Gold has been shown to display rich reactivity in combination with strained carbocycles, [15] and recently the ring-opening of alkylidene cyclopropanes by Au(III) was reported. [16]Therefore we wondered if Au(III) π-allyl complexes could be formed via a redox neutral rearrangement from their isomeric σ-cyclopropyl, driven by the release of strain energy. [12]o test this synthetic approach, the (P,C)-cyclometalated Au(III) σ-cyclopropyl complex 9 and the (P,N)-chelated Au(III) σcyclopropyl complex 10 were prepared (Scheme 3).For the rearrangement to proceed, a coordination site had to be liberated, which could be done by halide abstraction with AgSbF 6 .In both cases, the reaction led cleanly to the ringopened product.However, the temperature at which the rearrangement occurred depended strongly on the ligand used.For the (P,C)-cyclometalated Au(III) σ-cyclopropyl 9, the rearrangement occurred already at À 50 °C.Whereas the chelated biscationic (P,N)-chelated Au(III) σ-cyclopropyl complex 10 undergoes rearrangement already at À 80 °C and is complete when À 60 °C is reached.Changing the phenyl substituents on 9 to the more electron-donating cyclohexyl did not noticeably change the temperature at which the ring-opening proceeded.
The ring-opening process was investigated in-depth using DFT calculations.The free energy profile for the σ-cyclopropyl to π-allyl rearrangement for complex 9-Ph is given in Figure 2. The lowest barriers were found for the ring-opening where the distal σ(CC) bond was cleaved.For the (P,C) Au(III) σ-cyclopropyl complex, a barrier of 19.8 kcal/mol was found while for the (P,N) Au(III) σ-cyclopropyl complex, a lower activation barrier of 15.7 kcal/mol was found matching the experimental trend.Several other mechanistic pathways were considered, e. g. β-H elimination and insertion of Au into the σ(CC) bond, but these were found to not be energetically competitive.
A deeper look into the ring-opening process showed that the rotation of the two CH 2 moieties along the Intrinsic Reaction Coordinate (IRC) proceeds via a disrotatory ring-opening process.For analysis of the electron flow associated with the rearrangement, the intrinsic bond orbitals (IBO) were inspected.Here, the most noteworthy observation was the progressive conversion of the distal σ(CC) bond into a 3-center π-orbital (Figure 2), in line with an electrocyclic ring-opening.
Upon halide abstraction from σ-cyclopropyl complexes 9 and 10, a cationic coordinatively unsaturated Au(III) intermediate is formed.This type of complexes can engage in weak interactions such as agostic interactions with surrounding ligands or substrates. [17]In the case of the σ-cyclopropyl complexes, it can be envisioned that the σ(CC) bond engages in a donor-acceptor interaction with the gold center resulting in an agostic interaction.17a] Cyclopropyl has high ring strain resulting in bent banana bonds that are more prone to agostic interactions. [18]Natural Bond Orbital (NBO) analysis on the cationic 3-coordinate (P,C) Au(III) σ-cyclopropyl complex 9-Ph + showed donor-acceptor interactions with weak donations from the proximal and distal σ(CC) bonds to Au (2.9 and 4.6 kcal/mol, respectively).For the dicationic (P,N) Au(III) σ-cyclopropyl complex, similar agostic interactions were found, with donor-  acceptor interactions of 6.9 kcal/mol between the proximal σ(CC) bond and gold, and 6.4 kcal/mol between the distal σ(CC) bond and gold.
To demonstrate the versatility of the σ-cyclopropyl to π-allyl rearrangement, (N,C) cyclometalated complexes 12 were included in the study (Scheme 4).Like complexes 9 and 10, they undergo ring-opening upon liberation of a coordination site at gold.However, the rearrangement does not start before room temperature is reached, at which point the π-allyl complex decomposes, preventing a clean transformation.The rigidity of the backbone of the ancillary ligand (tolyl-pyridine versus benzoquinoline) did not influence the ring-opening to any significant degree, this observation was in good agreement with the calculated barriers for the ring-opening (27.1 and 26.4 kcal/mol for tolyl-pyridine and benzoquinoline, respectively).

Characterization and Structure of Au(III) π-Allyl Complexes
Complexes 3, 6 and 11 were unambiguously authenticated by multinuclear NMR spectroscopy. [8,9,11]Complexes 3 and 6 were also characterized by single crystal X-ray diffraction analysis.In the case of 6, connectivity was established, but twinning and disorder in the crystals led to poor data quality, thus the optimized structure for complex 6 will be used herein when comparing with the other π-allyl complexes.
The ancillary ligands employed in complexes 3, 6 and 11 have major differences in their electronic properties with the (P,C) ligand being close to electronically symmetric, whereas the (N,C) and (P,N) ligands are highly asymmetric due to P and C being significantly more donating than N.This difference is reflected in the bonding of the π-allyl moiety and thus the stability of the ensuing complexes (Table 1).Complex 3-iPr is stable at room temperature, whereas complexes 6 and 11 rapidly decompose at this temperature.
With the naphthyl-based (P,C) ligand employed in complexes 3, bench stable complexes were obtained featuring a quasi-symmetric η 3 coordination of the allyl moiety. [8]The symmetric coordination of the allyl in complex 3-iPr is illustrated by the equalization of the 13 C NMR chemical shifts of the two terminal carbons C a and C c of the π-allyl moiety (δ 83/76 versus δ 48/110 in the corresponding σ-allyl complex 2-iPr) together with the similar bond lengths found for C a À C b and C b À C c and the small variation found in the distance between Au and the three carbon atoms of the π-allyl moiety.In complexes 6 and 11, the picture is very different. [9,11,12]Here, the terminal carbons C a and C c are found at significantly different 13 C NMR chemical shifts (δ 50/106 for 6 and δ 67/115 for 11) indicating σ + π coordination of the allyl moiety where C a remains bonded in a σ-fashion, similarly to the σ-allyl precursors, and the double bond of the allyl moiety is π-coordinated to gold. [19]This is in line with the larger difference in trans influence (C > P @ N) of the two ends of the chelating ligand in complexes 6 and 11 compared to 3-iPr and the following thermodynamic preference of having the higher trans influence σ-end of the allyl moiety trans to the lower trans influence end of the ancillary ligand (aryl-N and ArMe 2 N in complexes 6 and 11, respectively).The asymmetric coordination of the allyl ligand was also observed in the optimized structures of complexes 6 and 11.In both cases C a is bound significantly tighter to gold compared to C b and C c , indicating significant σ-character of the AuÀ C a bond.Moreover, the bonding situation in complexes 3-iPr, 6 and 11 was analyzed by the atoms-in-molecules (AIM) approach showing noticeable differences between the different complexes (Table 2).For complex 3-iPr, bond critical points (BCP) are found between both the terminal carbons of the allyl ligand and gold, whereas for complexes 6 and 11, BCP is only found between gold and the terminal carbon of the allyl moiety trans to N (C a ).Furthermore, in complex 3-iPr, the associated electron densities (ρ) and the Bader's delocalization indexes (δ) are very similar, indicating a highly delocalized allyl moiety.In contrast, in complexes 6 and 11, very different values are obtained when comparing C a À C b and C b À C c , showing a significant double bond character for the latter bond.Table 1.Selected NMR, XRD and DFT data for complexes 3-iPr, 6 and 11 illustrating their striking differences in bonding. [8,9,11,12]he dynamic properties of π-allyl complexes play an important role when they are employed in catalysis. [7]The large electronic dissymmetry provided by the ancillary ligand and the following σ + π coordination of the allyl moiety observed in complexes 6 and 11 may point towards a higher fluxionality in these complexes, but this was only observed experimentally for complex 6. [9,11,12] DFT calculations showed that for complex 6, the η 1 forms are ca 12 kcal mol À 1 higher in energy than the η 3 form, and the free energy barriers for the involved coordination, rotation and re-coordination processes are not too high (< 18 kcal/mol).The dynamic behavior of complex 6 was evident from its 1 H NMR spectrum.The two protons H a are found as one resonance in contrast to what is normally observed in π-allyl complexes (including that of 3 and 11, see Table 1).This phenomenon indicates that double bond decoordination followed by rotation around the AuCH 2 -CHCH 2 and re-coordination occurs relatively fast at the NMR timescale leading to the coalescence of the two H a resonances.The same phenomenon was not observed for the two H c , indicating that the η 3 -η 1 -η 3 interconversion only occurs trans to Aryl-C in line with the asymmetric σ + π bonding of the allyl moiety with the thermodynamic preference of having the σ-character trans to Aryl-N.Lowering the temperature to ca À 80 °C, and thereby slowing down the η 3 -η 1 -η 3 interconversion process, led to the observation of the coexisting η 3 (with the resonances of the two H a now decoalesced) and η 1 forms of complex 6.In contrast, for complex 11, the difference in free energy between the η 3 and η 1 forms ( ~G = 36.5 kcal mol À 1 ) is three times as large as that of 6, explaining why no fluxionality was observed for complex 11.

Reactivity and Catalytic Applications of Au(III) π-Allyl Complexes
Nucleophilic addition to π-allyl complexes is a key elementary step in transition metal catalysis, most notably in the wellknown Pd-catalysed Tsuji-Trost reaction. [7]Most common is the outer-sphere nucleophilic addition to one of the terminal positions of the π-allyl (Scheme 5a, path I) leading to π-alkene complexes and ultimately the allylation products.The nucleophilic addition can also occur at the metal itself leading to σ-allyl complexes which can then undergo reductive elimination to release the allylation product (Scheme 5a, path II).Less common, but present in the literature, is the nucleophilic addition to the central position of the π-allyl leading to the formation of a metallacyclobutane (Scheme 5a, path III). [20,21]he reactivity of Au(III) π-allyl complexes 3 towards β-diketo enolates 14 was thoroughly investigated. [8,10]In all cases studied, the desired allylation products 15 originating from nucleophilic addition to the terminal position of the π-allyl were ultimately obtained in good yields (71-99 %) together with the Au(I) dimer 16 (Scheme 5b).However, after close inspection of these Table 2. Atoms-in-molecules (AIM) molecular graphs for complexes 3-iPr, 6 and 11 with relevant bond paths, bond critical points (BCP, green circles), electron densities (ρ in e bohr À 3 ) and delocalization indexes (δ).reactions both experimentally and computationally, they turned out to be much more complex than first anticipated.Nucleophilic addition to all sites (paths I, II and III) turned out to be possible and competitive.Four combinations of Au(III) π-allyl complexes 3 and nucleophiles 14 were studied in detail by multinuclear low temperature NMR spectroscopy and DFT calculations.It was found that, depending on the combination of Au(III) π-allyl complex and nucleophile, additions to all the different positions were indeed possible and complexes 17-19 could all be authenticated in solution by NMR spectroscopy.Complexes 17 and 19 were also isolated and characterized crystallographically and by high resolution mass spectrometry (HRMS).NMR spectroscopy together with DFT calculations showed that the nucleophilic additions to the central position of the π-allyl and to gold itself were reversible, explaining why ultimately, the coupling products 15 originating from the nucleophilic addition to the terminal position is observed in all cases studied.
The reaction of the Au(III) π-allyl complex 3-iPr-Me with the β-diketo enolate 14 a was the most complex, but also the most fascinating.In this case, nucleophilic addition to all possible sites could be authenticated within the same reaction (Scheme 6).Initially, the formation of σ-allyl complex 18 and auracyclobutane 20 (in a 3/2 ratio) was observed.Warming the reaction mixture to 25 °C for ca.30 min before cooling back to À 20 °C led to the quantitative formation of Au(I) π-alkene complex 21.Finally, the C-allylated product 15 a was released from the Au(I) π-alkene complex 21 at room temperature with concomitant formation of Au(I) dimer 16.
As mentioned previously, nucleophilic addition to the terminal position of Pd(II) π-allyl complexes usually dominates, and nucleophilic addition to the central position remains a curiosity. [20,21]To rationalize the different reactivity of Pd(II) and Au(III) π-allyl complexes, the Molecular Orbitals relevant for the nucleophilic additions to [(P,C)Au(π-allyl)] + 3-iPr and the related [(Ph 3 P) 2 Pd(II)(π-allyl)] + complex 3-Pd were computed (see Figure 3 for selected data). [10]Significant differences between the Au(III) and Pd(II) π-allyl complexes were discovered.While in both cases, the LUMO has large contributions on the terminal carbons (C term ) and the metal itself, only in 3-iPr vacant orbitals with significant contributions of the central carbon (C cent , 15.5 %) can be found at accessible energies (LUMO + 2, only 0.6 eV above the LUMO).In contrast, for complex 3-Pd, it is not before LUMO + 15, lying 2.2 eV above the LUMO, where a significant participation of C cent is found.This explains why nucleophilic attack to the central position of the π-allyl and formation of auracyclobutanes is so much more favourable than palladacyclobutanes.
The limited stability of (N,C) Au(III) π-allyl complex 6 prevented its reactivity towards nucleophiles to be studied in detail.However, attempts at obtaining single crystals of a gemdimethylallyl complex led to the authentication of a water adduct which may result from nucleophilic addition to the central position of the π-allyl followed by protodeauration. [22]he stoichiometric reaction of (P,C) Au(III) π-allyl complexes 3 with carbon based nucleophiles demonstrated the feasibility of CÀ C bond formation via nucleophilic attack to Au(III) π-allyls.While being fundamentally interesting, it was not a synthetically relevant method for CÀ C bond formation due to the use of stoichiometric amounts of gold.In order to achieve catalytic allylation via Au(III) π-allyl intermediates, a Au(I)/Au(III) redox cycle was envisioned similar to Ir, Ru and Pd catalysts.Here, (P,N) Au(III) π-allyl complexes were considered as good candidates as the (P,N) ligand enable to cycle between Au(I)/ Au(III) as has been shown to great success in catalytic CÀ C, CÀ N and CÀ S coupling reactions. [14]o demonstrate the feasibility of CÀ C coupling, the (P,N) Au(III) π-allyl complex 11 was reacted with one equivalent of Nphenyl indole as a synthetically relevant nucleophile (Scheme 7). [11]The C3 allylated product was obtained as the Scheme 6. Reaction of the π-allyl Au(III) complex 3-iPr-Me with the β-diketo enolate 14 a.only product, as expected with the more nucleophilic nature of the C3 position of indoles.The ability of the Me-Dalphos ligated Au complex to cycle through Au(I)/Au(III) catalytic cycles combined with the formation of a single product in the stoichiometric reaction made it a good candidate for catalytic allylation.
After optimization of the reaction conditions, it was found that the allylation could proceed with catalytic amounts of (P,N)AuCl (Scheme 8).For the catalytic transformation, AgSbF 6 was used to carry out the functions of both halide abstraction from the initial (P,N)AuCl and to replace BCF as a Lewis acid to promote the oxidation of the π-alkene complex.While the transformation worked well with a variety of allyl substrates (alcohols, acetates, carbonates, phosphates and halides), the investigation of the scope was achieved on allyl acetates and alcohols which are the most valuable synthetically.Control experiments showed that it was indeed the gold catalyst that promoted the reaction and only traces of the allylation product were observed without it.
To provide further proof for the involvement of Au(III) π-allyl intermediates in the catalytic reaction, α and γ substituted allyl alcohols and acetates were investigated (Scheme 8).It was expected that the same ratio for linear and branched products is obtained if the reaction proceeds via π-allyl intermediates as is observed with Pd, Ir, Rh catalysts. [23]Subjecting the α and γ substituted allyls to the catalytic conditions indeed resulted in the formation of the same branched C3 allylated indoles independently of whether the α or γ position was substituted on the initial allyl.All tested substrates were completely selective for the branched isomer, with the exception of ethyl allyl acetate where a 95 : 5 ratio was obtained.To further probe the generality of the transformation, substituted α phenyl allyl acetates were tried with indoles containing different substitutions on the nitrogen and indole backbone.In all cases, complete selectivity for the C3 allylated branched product was observed with good to excellent yields (62-92 %).Only when the C3 position of the indole was sterically hindered or the nucleophilicity lowered with electron withdrawing groups were lowered yields observed (35-56 %).Good functional group compatibility was observed with the reaction tolerating CÀ F, CÀ Br and CÀ Si bonds.14a] The selectivity for the branched product could be elucidated when the Au(III) π-allyl intermediate was investigated computationally.The most stable optimized structure for the methyl substituted π-allyl was found with the Me group in the pseudoequatorial position, trans to the phosphorus (Figure 4).The LUMO showed a higher contribution to this carbon (20.7 %) compared to the carbon cis to the phosphorus (13.9 %).The higher contribution of the LUMO combined with the easier accessibility due to the less sterically demanding NMe 2 groups compared to the PAd 2 group offer an explanation to the observed selectivity for the branched product.When comparing these results with earlier reports on the allylation of indoles via transition metal π-allyls, the complementary nature of Au becomes clear.In the allylation of indoles with Pd catalysts, the linear product is obtained, while with Ir, usually branched products are observed.As for Ru catalysts, the selectivity is highly dependent on the ligand, with selectivities in favour of both the linear and branched product being reported as well as the formation of mixtures. [23]

Summary and Outlook
During the last three years, Au(III) π-allyl complexes have emerged as a very interesting and attractive class of compounds.The use of (P,C), (N,C) and (P,N) bidentate ligands was shown to impart enough stability to enable the characterization or even the isolation of such complexes.Various synthetic routes, with or without oxidation of gold, have been developed.Detailed analyses of their structure revealed either symmetric η 3 or asymmetric σ + π-coordination of the allyl moiety to gold, depending on the ancillary ligand.Rich reactivity towards nucleophiles was also substantiated, with possible additions to the terminal and central positions of the π-allyl, as well as to gold itself.The possibility to achieve catalytic transformation via Au(III) π-allyl complexes has also been demonstrated.Most noteworthy are the specific features of the Au(III) π-allyl complexes, compared to the isoelectronic Pd(II) species, making them valuable tools.
These first achievements are very exciting and for sure, much remains to be discovered and developed when it comes to Au(III) π-allyl complexes.The variety of ancillary ligands at Au(III) can certainly be further expanded, enabling  to finely tune the structure and reactivity of the π-allyl moiety at Au(III). [13]Other catalytic transformations than the allylation of indoles are also most probably achievable via Au(III) π-allyl complexes.Selectivities complementary to the other transition metals may be encountered and transformations involving nucleophilic attack to the central position of the π-allyl may be developed.26]

David
Vesseur obtained his bachelor degree in 2018 at the University of Amsterdam (UVA) and Vrije Universiteit Amsterdam (VU), he then continued his studies at the UVA to obtain his master degree in 2020, during this he spend one year in the research group of Dr. Bas de Bruin developing new ways to access Co(III) carbene radicals.In 2020, he started his PhD under the supervision of Dr. Didier Bourissou at the Laboratoire Hétérochimie Fondamentale et Appliquée (LHFA).His research focuses on ligand-enabled Au(I)/Au-(III) oxidation and the stabilization of coinage metal carbenes.Marte Sofie Martinsen Holmsen obtained her master degree in 2013 from the University of Oslo, Norway, where she worked with Nheterocyclic carbene complexes under the supervision of Professor Mats Tilset.She then pursued her PhD in the same group working with fundamental studies on cyclometalated Au(III) complexes.In 2020, she moved to Toulouse, France, where she did a postdoc with Dr. Didier Bourissou at the Laboratoire Hétérochimie Fondamentale et Appliquée (LHFA).In 2021 she was awarded a FRINATEK mobility grant from the Reseach Council of Norway for a two years postdoctoral stay in the group of Dr. Didier Bourissou and thereafter a year in the group of Professor Mats Tilset.Didier Bourissou obtained his PhD from Toulouse University.He then spent one year as research associate at the Ecole Polytechnique.Appointed as a Chargé de Recherche CNRS in 1998, he was promoted Directeur de Recherche in 2006.From 2006 to 2018, he has been Associate Professor at the Ecole Polytechnique.He has been Director of the Laboratoire Hétérochimie Fondamentale et Appliquée (LHFA) from 2011 to 2020.He was awarded the Bronze (2005) and Silver (2016) Medals of the CNRS, the Clavel Lespiau Distinction (2006) and Del Duca Grant (2020) from the French Academy of Sciences, the Acros (2009) and Organic Division (2018) Awards from the French Chemical Society in recognition of his work.His research interests concern new bonding situations and reactivity patterns arising from the main group elements, the transition metals and their interplay.He has pioneered ambiphilic ligands in the mid 2000's and developed the concept of σ-acceptor ligands.Part of his research deals with non-innocent pincer complexes and in biodegradable polymers (ring-opening polymerization, organic and dual catalysis, drug delivery systems).He is also very much interested in the organometallic chemistry and catalytic applications of the coinage metals, in particular gold.He has been awarded an ERC Advanced grant in 2023 to explore Gold-Redox chemistry.

Scheme 1 .
Scheme 1. Preparation of Au(III) π-allyl complexes 3 and 6 (OAc F = OCOCF 3 ) upon halide abstraction from σ-allyl complexes 2 and 5.The yields given for complex 2 and 3 are for R = iPr and R ' = H.No yield reported for 6 as it starts to decompose at the same time as it forms.

Figure 2 .
Figure 2. Computed energy profile for the ring-opening of the (P,C) Au(III) σcyclopropyl complex 9-Ph to give the corresponding π-allyl complex 3-Ph.ΔG values in kcal/mol, main distances in Å. Profile computed in the gas phase at the B3PW91/SDD + f(Au), 6-31G** (other atoms) level of theory and main IBOs accounting for the ring-opening of the distal σ(CC) bond along the reaction path (numbers relate to the fraction of electrons of the doubly occupied orbital assigned to each atom).

Scheme 5 .
Scheme 5. (a) Possible reactive sites for the nucleophilic addition to transition metal π-allyl complexes.(b) Reactivity of complexes 3 (R = iPr or Cy, R' = H or Me) towards β-diketo enolates 14 (R'' = OEt, OtBu or Ph).(c) Examples of characterized complexes (17-19) showing nucleophilic addition to the central and terminal position of the π-allyl, as well as to gold.

Figure 3 .Scheme 7 .
Figure 3. Key Molecular Orbitals (MO) computed for complexes 3-iPr and 3-Pd.Energy of the MOs in eV, cutoff: 0.05.Contribution of the main atoms in each MO in %.