E-H Bond Activation and Insertion Processes in the Reactions of the Unsaturated Hydride [W₂Cp₂(μ-H)(μ-PPh₂)(NO)₂]

The reactions of the title complex (1) with different p-block element (E) molecules was examined. Compound 1 reacted with BH₃·THF at room temperature to give the trihydride [W₂Cp₂(μ-H)H₂(μ-PPh₂)(NO)₂], which formally results from hydrogenation of 1, a reaction that actually does not take place when neat dihydrogen is used. Clean E-H bond oxidative addition, however, took place when 1 was reacted with HSnPh₃, to give the related dihydride stannyl derivative [W₂Cp₂(μ-H)H(μ-PPh₂)(NO)₂(SnPh₃)]. In contrast, the reaction of 1 with HSPh involved H₂ elimination to give the thiolate-bridged complex [W₂Cp₂(μ-SPh)(μ-PPh₂)(NO)₂], while that with (p-tol)C(O)H resulted in insertion of the aldehyde to yield the related alkoxide complex [W₂Cp₂{μ-OCH₂(p-tol)}(μ-PPh₂)(NO)₂]. Insertion also prevailed in the reactions of 1 with CN^tBu, which, however, involved the competitive formation of new C-H or N-H bonds, to give a mixture of formimidoyl and aminocarbyne derivatives, [W₂Cp₂(μ-κ¹:η²-HCN^tBu)(μ-PPh₂)(NO)₂] (W-W = 3.0177(2) Å) and [W₂Cp₂{μ-C(NH^tBu)}(μ-PPh₂)(NO)₂] (W-W = 2.9010(4) Å), respectively, even though the latter was thermodynamically preferred, according to density functional theory calculations. The former represents the first structurally characterized complex displaying a formimidoyl or iminoacyl ligand in the alkenyl-like μ-κ¹:η² coordination mode. The reaction of 1 with diazomethane proceeded with N₂ elimination and C-H coupling to yield the agostic methyl-bridged complex [W₂Cp₂(μ-κ¹:η²-CH₃)(μ-PPh₂)(NO)₂] (calculated W-W = 2.923 Å), whereas the reaction with N₂CH(SiMe₃) proceeded with insertion of the diazoalkane to give the corresponding hydrazonide complex [W₂Cp₂{μ-NH(NCHSiMe₃)}(μ-PPh₂)(NO)₂] (W-W = 2.8608(4) Å). The latter was converted under alkaline conditions to the methyldiazenide derivative [W₂Cp₂{μ-N(NMe)}(μ-PPh₂)(NO)₂] (W-W = 2.8730(2) Å), in a process involving hydrolysis of the C-Si bond coupled with a 1,3-H shift from N to C.