Synthesis and characterization of trinuclear osmium clusters containing diallylphosphines as hemilabile ligands: Experimental and theoretical studies of their reactivity with nucleophilic molecules

A series of [Os3(CO)12] phosphine substituted derivatives containing alkenylphosphine ligands has been synthesized starting from the cluster [Os3(CO)10(MeCN)2] and RP(CH2CHCH2)2 where R = iPr2N, o‒MeOC6H4 or p−MeOC6H4. It was shown that the terminal alkenyl substituent in these phosphines undergoes coordination at the metal triangle to give the allyl fragment coordinated through the double bond. Solid–state structures of [Os3(CO)10{μ:κ3(P,C,C)–RP(CH2CCH2)2}] [R = iPr2N (1a), o–MeOC6H4 (1c)], [Os3(CO)10{κ1(P)–iPr2NP(CH2CCH2)2}L] [L = CO (3a), PPh3 (4a)], [Os3(CO)9(PPh3){μ:κ3(P,C,C)–iPr2NP(CH2CCH2)2}] (5a) and [Os3(CO)10(μ:η1:η3–C3H4){κ1(P)–p–MeOC6H4P(CH2CCH2)2}] (6b) were established by X–ray crystallography; all products obtained were also characterized by IR and NMR (1H, 13C{1H}, 31P{1H}, 1H–1H and 1H–13C correlations) spectroscopy. It was shown that [Os3(CO)10{μ:κ3(P,C,C)–(diallylphosphine)}] compounds in solution are present as a mixture of isomers; this isomerization is described as a reorientation of the coordinated double bond respect to the triosmium metal triangle. Also, reactivity studies were performed with CO, PPh3 and C3H4, establishing the hemilabile properties of the diallyphosphine ligands with the cleavage of the allyl π–coordination when the nucleophilic molecules are CO and PPh3; in contrast, the nucleophile C3H4 leads to cleavage and insertion of the allene into the Os–Os bond.