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

Abstract

This article describes the differing chemical properties imparted by the two ligands, hemilabile 2-[(diisopropylphosphino)methyl]-3-methylpyridine (PrPN) and the related 1,2-bis(dimethylphosphino)ethane (dmpe), when attached to the 14e Cp*M(NO) scaffolds (Cp* = η-CMe; M = W, Mo). For instance, the treatment of [Cp*W(NO)Cl] with 2 or 1 equiv of dmpe in CH affords excellent yields of [Cp*W(NO)(κ-dmpe)Cl]Cl (1) or [Cp*W(NO)Cl][μ-dmpe] (2). In contrast, the treatment of [Cp*W(NO)Cl] with 1 equiv of PrPN in CH does not produce the complex analogous to 1 but rather affords orange [Cp*W(NO)(κ-P-N-PrPN)Cl][Cp*W(NO)Cl] (3) in 90% yield. Furthermore, subsequent reduction of 1 or 2 with 2 or 4 equiv of CpCo in tetrahydrofuran (THF), respectively, results in the production of orange Cp*W(NO)(κ-dmpe) (4) in good yields. However, a similar treatment of 3 with 1 equiv of CpCo in THF does not result in the production of Cp*W(NO)(κ-P,N-PrPN), the analogue of 4, but rather generates a 1:1 mixture of the novel complexes Cp*W(NO)(H)(κ-P-PrPN)Cl (5) and Cp*W(NO)(κ-P,N-PrPCH-2-(3-Me-CHN))Cl (6), which are separable by crystallization from pentane and diethyl ether solutions, respectively. The divergent reactivity imparted by the dmpe and PrPN 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)Cl] with 2 equiv of PrPN in CH first forms Cp*Mo(NO)(κ-P-PrPN)Cl, which then converts to [Cp*Mo(NO)(κ-P,N-PrPN)Cl][Cp*Mo(NO)Cl], the analogue of 3. Reduction of the Cp*Mo(NO)(κ-P-PrPN)Cl intermediate complex with 2 equiv of CpCo affords dark-green Cp*Mo(NO)(κ-P,N-PrPN) (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.