Dimolybdenum Cyclopentadienyl Complexes with Bridging Chalcogenophosphinidene Ligands

The reactions of the phosphinidene-bridged complex [Mo2Cp2(μ-PH)­(η6-HMes*)­(CO)2] (1), the arylphosphinidene complexes [Mo2Cp2(μ-κ1:κ1,η6-PMes*)­(CO)2] (2), [Mo2Cp2(μ-κ1:κ1,η4-PMes*)­(CO)3] (3), [Mo2Cp2(μ-κ1:κ1,η4-PMes*)­(CO)2(CNtBu)] (4), and the cyclopentadienylidene-phosphinidene complex [Mo2Cp­(μ-κ1:κ1,η5-PC5H4)­(η6-HMes*)­(CO)2] (5) toward different sources of chalcogen atoms were investigated (Mes* = 2,4,6-C6H2tBu3; Cp = η5-C5H5). The bare elements were appropriate sources in all cases except for oxygen, in which case dimethyldioxirane gave the best results. Complex 1 reacted with the mentioned chalcogen sources at low temperature, to give the corresponding chalcogenophosphinidene derivatives [Mo2Cp2{μ-κ2P,Z:κ1P-ZPH}­(η6-HMes*)­(CO)2] (Z = O, S, Se, Te; P–Se = 2.199(2) Å). The arylphosphinidene complex 2 was the least reactive substrate and gave only chalcogenophosphinidene derivatives [Mo2Cp2(μ-κ2P,Z:κ1P,η6-ZPMes*)­(CO)2] for Z = O and S (P–O = 1.565(2) Å), along with small amounts of the dithiophosphorane complex [Mo2Cp2(μ-κ2P,S:κ1S′,η6-S2PMes*)­(CO)2], in the reaction with sulfur. The η4-complexes 3 and 4 reacted with sulfur and gray selenium to give the corresponding derivatives [Mo2Cp2(μ-κ2P,Z:κ1P,η4-ZPMes*)­(CO)2L] (L = CO, CNtBu), obtained respectively as syn (Z = Se; P–Se = 2.190(1) Å for L = CO) or a mixture of syn and anti isomers (Z = S; P–S = 2.034(1)–2.043(1) Å), with these diastereoisomers differing in the relative positioning of the chalcogen atom and the terminal ligand at the metallocene fragment, relative to the Mo2P plane. The cyclopentadienylidene compound 5 reacted with all chalcogens, and gave with good yields the chalcogenophosphinidene derivatives [Mo2Cp­(μ-κ2P,Z:κ1P,η5-ZPC5H4)­(η6-HMes*)­(CO)2] (Z = S, Se, Te), these displaying in solution equilibrium mixtures of the corresponding cis and trans isomers differing in the relative positioning of the cyclopentadienylic rings with respect to the MoPZ plane in each case. The sulfur derivative reacted with excess sulfur to give the dithiophosphorane complex [Mo2Cp­(μ-κ2P,S:κ1S′,η5-S2PC5H4)­(η6-HMes*)­(CO)2] (P–S = 2.023(4) and 2.027(4) Å). The structural and spectroscopic data for all chalcogenophosphinidene complexes suggested the presence of a significant π­(P–Z) bonding interaction within the corresponding MoPZ rings, also supported by Density Functional Theory calculations on the thiophosphinidene complex syn-[Mo2Cp2(μ-κ2P,S:κ1P,η4-SPMes*)­(CO)3].