Synthesis, spectroscopic characterization and structural studies of bromodioxodimethylsulfoxide (N,N′-dialkyldithiocarbamates and O-alkyl dithiocarbonate)molybdenum(VI) complexes: Crystal structures of MoO2Br2(OSMe2)2 and MoO2Br2(C12H8N2) · CH2Cl2
Graphical abstract
Reactions of dibromodioxobis(dimethylsulfoxide)molybdenum(VI) with sodium/potassium salts of N,N′-dialkyl dithiocarbamates or O-alkyl dithiocarbonates yield bromodioxomolybdenum(VI) complexes of the type, MoO2Br(S2CNR2)(OSMe2) or MoO2Br(S2COR)(OSMe2). Crystals of MoO2Br2(OSMe2)2 and MoO2Br2(C12H8N2) · CH2Cl2 have distorted octahedral environments around molybdenum with two cis-oxygen atoms and two trans-bromine atoms in both along with two cis-dimethylsulfoxide moieties in the former and 1,10-phenanthroline in the latter.
Introduction
The potential role of high oxidation state oxomolybdenum(VI) complexes as model systems in molybdoenzymes [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], as oxo transfer agents [12] and as catalyst precursors e.g. in the selective epoxidation of olefins [13] prompted us to work with higher valent molybdenum complexes. In contrast to other metals active in biological systems, the oxidation state of molybdenum in such systems is generally high, usually +5 or +6. Crystal structures of MoO2X2 · 2OPPh3 (X = Cl, Br) [14], MoO2Cl2 · 2DMSO [15], [16] and model studies for molybdoenzymes on MoO2X2 · 2L (X = Cl, Br; L = OPPh3) have been reported [14]. An improved role in oxygen transfer reactions [9], [17] has been suggested for air stable dioxomolybdenum(VI) complexes derived from their air sensitive precursors MoO2Cl2 and MoO2Br2. Our continuing interest in oxomolybdenum(VI) complexes has led to this report on the reactions of dibromodioxobis(dimethylsulfoxide)molybdenum(VI) complexes with sodium or potassium salts of N,N-dialkyl dithiocarbamate and O-alkyl dithiocarbonate to yield complexes such as MoO2Br(S2CNR2)(OSMe2) and MoO2Br(S2COR)(OSMe2) along with their characterization by various spectroscopic techniques. We also report on the synthesis and X-ray crystal structures of MoO2Br2(OSMe2)2 and MoO2Br2(C12H8N2) · CH2Cl2.
Section snippets
Experimental
Na2MoO4 · 2H2O, dimethylsulfoxide and 1,10-phenanthroline were used as purchased from E. Merck. All solvents (methanol, ethanol, isopropanol, dichloromethane, and benzene) were dried by standard methods before use. Stringent precautions were taken to exclude moisture during experimental manipulations. Literature methods were used for the preparation of sodium or potassium salts of N,N-dialkyl dithiocarbamate [18] and O-alkyl dithiocarbonate [19].
Results and discussion
Reactions of dibromodioxobis(dimethylsulfoxide)molybdenum(VI) complexes with sodium/potassium salts of N,N′-dialkyl dithiocarbamates or O-alkyl dithiocarbonates in a 1:1 molar ratio in dichloromethane yield dioxomolybdenum(VI) complexes of the type, MoO2Br(S2CNR2)(OSMe2) or MoO2Br(S2COR)(OSMe2), respectively (see Fig. 3)MoO2Br2(OSMe2)2 + NaS2CNR2 → MoO2Br(S2CNR2)(OSMe2) + OSMe2 (Free) + NaBrwhere R = Et, Prn, PriMoO2Br2(OSMe2)2 + NaS2COR → MoO2Br(S2COR)(OSMe2) + OSMe2 (Free) + NaBrwhere R = Et, Prn, Pri.
All of
Concluding comments
We have successfully prepared and characterized the following bromodioxodimethylsulfoxide(N,N′-dialkyldithiocarbamate/O-alkyldithiocarbonate)molybdenum(VI) complexes, MoO2Br(S2CNR2)(OSMe2) (R = Et, Prn, Pri) and MoO2Br(S2COR)(OSMe2) (R = Et, Prn, Pri). The IR, UV–Vis and 1H NMR spectra of all of these dioxomolybdenum(VI) complexes are consistent with the proposal of the following tentative structure.
The molecular structures of MoO2Br2(OSMe2)2 and MoO2Br2(C12H8N2) · CH2Cl2 have been determined. They
Acknowledgements
Two of us (R.K. and R.R.) are grateful to UGC, New Delhi for financial support. M.B. Hursthouse thanks the UK Engineering and Physical Sciences Council for support of the X-ray facilities at Southampton University. J.E.D. wishes to thank the University of Windsor for financial support. We are also thankful to RSIC, CDRI, Lucknow for the spectral analyses.
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