Electronic Structure and Multisite Basicity of the Pyramidal Phosphinidene-Bridged Dimolybdenum Complex [Mo2(η5‑C5H5)(μ‑κ1:κ1,η5‑PC5H4)(η6‑C6H3 tBu3)(CO)2(PMe3)]

Abstract

The title phosphinidene complex could be sequentially protonated with HBF4·OEt2 or [H(OEt2)2](BAr′4) to give the phosphido-bridged derivatives [Mo2Cp(μ-κ1:κ1,η5-HPC5H4)(η6-HMes*)(CO)2(PMe3)]X and then the hydrides [Mo2Cp(H)(μ-κ1:κ1,η5-HPC5H4)(η6-HMes*)(CO)2(PMe3)]X2 (X = BF4, BAr′4; Ar′ = 3,5-C6H3(CF3)2; Mes* = 2,4,6-C6H2tBu3). Density functional theory (DFT)calculations revealed that the most favored site for initial electrophilicattack is the metallocene Mo atom, but attachment of the electrophile tothe phosphinidene P atom gives more stable products. This was inagreement with all other reactions investigated, which invariably involvedthe attachment of the added electrophile at the P site. Thus, the titlecompound reacted with S8 at 223 K to give the thiophosphinidenebridged complex [Mo2Cp{μ-κ1:κ1,η5-P(S)C5H4}(η6-HMes*)(CO)2(PMe3)], a poorly stable molecule which reacted with MeI at room temperature to give the corresponding thiolatophosphido derivative, isolated as [Mo2Cp{μ-κ1:κ1,η5-P(SMe)C5H4}(η6-HMes*)(CO)2(PMe3)](BAr′4) (P−S = 2.128(4) Å) after anion exchange with Na(BAr′4). Reaction of the title compound with MeI proceeded smoothly to give the corresponding methylphosphido derivative, isolated analogously as [Mo2Cp{μ-κ1:κ1,η5-P(Me)C5H4}(η6-HMes*)(CO)2(PMe3)](BAr′4). The related complex [Mo2Cp{μ-κ1:κ1,η5-P(Me)C5H4}(η6-HMes*)(CO)2(PMe2Ph)](BAr′4) (P−C(Me) = 1.841(5) Å) could be prepared analogously from the neutral precursor [Mo2Cp{μ-κ1:κ1,η5-PC5H4}(η6-HMes*)(CO)2(PMe2Ph)]. In contrast, reaction of the title complex with ethylene sulfide involved opening of the C2S ring and formation of new P−C and Mo−S bonds (1.886(7) and 2.493(2) Å, respectively), with displacement of the PMe3 ligand, to give the phosphido−thiolato complex [Mo2Cp{μ-κ2P,S:κ1P,η5-P(C2H4S)C5H4}(η6-HMes*)(CO)2]. All these derivatives of the title complex displayed an unusual trigonal pyramidal-like environment around the bridging P atom, with the added electrophile placed in the Mo2P plane as a result of the directionality of the relevant frontier orbital of the phosphinidene complex, according to DFT calculations.