Isonitrile Insertion into Titanium Neopentylidene Alkyl Complexes Yields a Bifurcated Pathway to Form κ1-N-vinylamido or κ2-C,N-azaalleneyl Fragments

Abstract

Three organometallic ligand scaffolds resulting from the insertion of 1-adamantyl isonitrile (C≡NAd; Ad = C₁₀H₁₅) into titanium neopentylidene complexes, [(PNP)Ti═CH^tBu(X)] are described herein. Treatment of the titanium neopentylidene complex (PNP)Ti═CH^tBu(OTf) (1-OTf, PNP^– = N[2-PⁱPr₂-4-methylphenyl]₂^–, OTf = trifluoromethanesulfonate^–) with one equivalent of C≡NAd leads to the formation of a titanium η²-C,N-ketenimine, (PNP)Ti(η²-C,N-AdNCCH^tBu)(OTf) (2-OTf). However, when the titanium neopentylidene neopentyl complex (PNP)Ti═CH^tBu(CH₂^tBu) (1-Np) is added one equivalent of C≡NAd, a titanium neopentylidene κ¹-N-vinylamido complex (PNP)Ti═CH^tBu(κ¹-N-AdNCHCH^tBu) (3) is formed. In contrast, the titanium neopentylidene methyl complex (PNP)Ti═CH^tBu(CH₃) (1-Me) reacts with one equivalent of C≡NAd to produce a rare chelating κ²-C,N-azaalleneyl ligand, in the complex (PNP)Ti(κ²-C,N-AdNCC^tBu) (4), with concurrent extrusion of methane. Independently, it is shown that treatment of 2-OTf with one equivalent of neopentyl lithium (LiNp, Np^– = CH₂^tBu) or a half equivalent of dimethyl magnesium (MgMe₂) smoothly forms complex 3 or 4, respectively, and suggests that the η²-C,N-ketenimine ligand in 2-OTf might be an intermediate ligand enroute to the neopentylidene κ¹-N-vinylamido or κ²-C,N-azaalleneyl complexes. Complexes 2-OTf, 3 and 4 have been structurally and spectroscopically characterized and a proposed mechanism for the formation of complexes 3 and 4 is also described.