Sn–H bond additions to asymmetric trigonal phosphinidene-bridged dimolybdenum complexes

Abstract

The reactions between organotin hydrides HSnR₃ (R = Bu, Ph) and the asymmetric trigonal phosphinidene-bridged complexes [Mo₂Cp(μ-κ¹:κ¹,η⁵-PC₅H₄)(CO)₂(η⁶-HMes*)] (1), [Mo₂Cp₂(μ-PH)(CO)₂(η⁶-HMes*)] (2), and [Mo₂Cp₂(μ-PMe)(CO)₂(η⁶-HMes*)] (3) were examined, and found to be strongly dependent on the parent complex (Mes* = 2,4,6-C₆H₂^tBu₃). Compound 1 reacted with HSnR₃ upon moderate heating (353–363 K), to give the corresponding derivatives [Mo₂Cp{μ-κ¹:κ¹,η⁵-P(H)C₅H₄}(SnR₃)(CO)₂(η⁶-HMes*)], following from a formal 1,2-addition of the Sn–H bond across the Mo–P double bond of the parent complex, with specific formation of Sn–Mo and H–P bonds. Complex 2 reacted analogously, but much faster, to yield the corresponding phosphanyl-bridged derivatives [Mo₂Cp₂(μ-PH₂)(SnR₃)(CO)₂(η⁶-HMes*)] at room temperature. However, these products progressively degraded to the corresponding mononuclear phosphine complexes trans-[MoCp(SnR₃)(CO)₂(PH₃)] in the presence of trace amounts of water. The methylphosphinidene-bridged complex 3 (Mo–P = 2.550(3) and 2.281(3) Å) was prepared upon reaction of MeLi with the phosphide-bridged complex [Mo₂Cp₂(μ-P)(CO)₂(η⁶-HMes*)](BAr′₄), (Ar′ = 3,5-C₆H₃(CF₃)₂). Its reaction with HSnR₃ proceeded at room temperature with H–Sn bond addition now accompanied by spontaneous dehydrogenation, to yield the corresponding cyclopentadienylidene–phosphanyl derivatives [Mo₂Cp{μ-κ¹:κ¹,η⁵-P(Me)C₅H₄}(SnR₃)(CO)₂(η⁶-HMes*)]. The structures of the new complexes were analyzed using spectroscopic, diffractometric and, in some cases, density functional theory methods. The Sn–H bond cleavages leading to the complexes eventually isolated in these reactions were proposed to be initiated by σ-bond coordination of the organotin reagent, via its Sn–H bond, to the metal atom of the MoCp(CO)₂ fragment in the parent compounds, this being followed by a H-shift to the P atom of the bridging phosphinidene ligand.