Effects of Coordinating a Hemilabile Ligand to 14e Cp*M(NO) Scaffolds (M = Mo, W)

This article describes the differing chemical properties imparted by the two ligands, hemilabile 2-[(diisopropylphosphino)methyl]-3-methylpyridine (ⁱPr₂PN) and the related 1,2-bis(dimethylphosphino)ethane (dmpe), when attached to the 14e Cp*M(NO) scaffolds (Cp* = η⁵-C₅Me₅; M = W, Mo). For instance, the treatment of [Cp*W(NO)Cl₂]₂ with 2 or 1 equiv of dmpe in C₆H₆ affords excellent yields of [Cp*W(NO)(κ²-dmpe)Cl]Cl (1) or [Cp*W(NO)Cl₂]₂[μ-dmpe] (2). In contrast, the treatment of [Cp*W(NO)Cl₂]₂ with 1 equiv of ⁱPr₂PN in C₆H₆ does not produce the complex analogous to 1 but rather affords orange [Cp*W(NO)(κ²-P-N-ⁱPr₂PN)Cl][Cp*W(NO)Cl₃] (3) in 90% yield. Furthermore, subsequent reduction of 1 or 2 with 2 or 4 equiv of Cp₂Co in tetrahydrofuran (THF), respectively, results in the production of orange Cp*W(NO)(κ²-dmpe) (4) in good yields. However, a similar treatment of 3 with 1 equiv of Cp₂Co in THF does not result in the production of Cp*W(NO)(κ²-P,N-ⁱPr₂PN), the analogue of 4, but rather generates a 1:1 mixture of the novel complexes Cp*W(NO)(H)(κ¹-P-ⁱPr₂PN)Cl (5) and Cp*W(NO)(κ²-P,N-ⁱPr₂PCH-2-(3-Me-C₅H₃N))Cl (6), which are separable by crystallization from pentane and diethyl ether solutions, respectively. The divergent reactivity imparted by the dmpe and ⁱPr₂PN proligands is a unique demonstration of the unusual properties of a mixed-donor ligand. In the case of molybdenum, the reaction of [Cp*Mo(NO)Cl₂]₂ with 2 equiv of ⁱPr₂PN in C₆H₆ first forms Cp*Mo(NO)(κ¹-P-ⁱPr₂PN)Cl₂, which then converts to [Cp*Mo(NO)(κ²-P,N-ⁱPr₂PN)Cl][Cp*Mo(NO)Cl₃], the analogue of 3. Reduction of the Cp*Mo(NO)(κ¹-P-ⁱPr₂PN)Cl₂ intermediate complex with 2 equiv of Cp₂Co affords dark-green Cp*Mo(NO)(κ²-P,N-ⁱPr₂PN) (7). All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses.