The tetraphosphane all transtetrakis-(di(2-methoxyphenyl)phosphanyl)cyclobutane) (o-MeO-dppcb) has been employed to coordinate metal dichlorides (metal = Ni^II, Pd^II and Pt^II), stereoselectively yielding the dinuclear complexes [Ni₂Cl₄(μ-(κP¹:κP²:κP³:κP⁴-o-MeO-dppcb))] (3a₆6) and [Pt₂Cl₄(μ-(κP¹,κP²:κP³,κP⁴-o-MeO-dppcb))] (2a₅5), characterized by two six and two five-membered metallacycles, respectively. Conversely, the reaction with PdCl₂ led, under comparable synthetic conditions, to the formation of the linkage-isomeric pair [Pd₂Cl₄(μ-(κP¹,κP²:κP³,κP⁴-o-MeO-dppcb))] (1a₅5) and [Pd₂Cl₄(μ-(κP¹:κP²:κP³:κP⁴-o-MeO-dppcb))] (1a₆6) in a ca. 4 : 1 ratio. The compounds obtained have been characterized in solution by multinuclear NMR spectroscopy and in the solid state by CP-MAS NMR spectroscopy, XRPD and single crystal X-ray diffraction. Compounds 1a₅5 and 1a₆6 have been tested as catalyst precursors for the CO–ethene–propene co-and terpolymerization in water–acetic acid mixtures. Their catalytic performance has been compared to that of [PdCl₂(o-MeO-dppe)] (1b) (o-MeO-dppe = 1,2-(bis(di(2-methoxyphenyl)phosphanyl))ethane) and of [PdCl₂(o-MeO-dppp)] (1c) (o-MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane). The most striking result that emerged from the CO–ethene copolymerization study was that 1a₅5 was three times more productive than 1a₆6, outperforming, under identical catalytic conditions, even 1b and 1c, that are classified amongst the most active catalysts for the CO–ethene copolymerization reaction.