Disruption of the π-perpendicular component of a 4-electron donor alkyne ligand in a high-valent complex of tungsten by introduction of an organoimido ligand

Abstract

Addition of Me3SiNHCMe3 to the 4-electron donor alkyne complex [{WCl4(PhC2Ph)}2] gave [{WCl2(NCMe3)(PhC2Ph)(NH2CMe3)}x] 1 for which the acetylenic carbon resonance position, δ 156.23, in the 13C-{1H} NMR spectrum indicated a 2-electron donor alkyne. Small changes in δ for derivatives [NEt4][WCl3(NCMe3)(PhC2Ph)(NH2CMe3)] 2 (161.28), trans-dichloro complexes [WCl2(NCMe3)(PhC2Ph)(bipy)] 3 (bipy = 2,2′-bipyridyl, δ 163.60) and [WCl2(NCMe3)(PhC2Ph)(dmbipy)] 4 (dmbipy = 4, 4′-dimethyl-2,2′-bipyridyl, δ 162.93) as well as cis-dichloro complexes [WCl2(NCMe3)(PhC2Ph)(py)2] 5 (py = pyridine, δ 155.78), [WCl2(NCMe3)(PhC2Ph)(PMe3)2] 6 (δ 151.15) and [WCl2(NCMe3)(PhC2Ph)(PMe2Ph)2] 7 (δ 153.37) indicate small electronic differences in the alkyne–metal bonding. A crystal structure determination of 6 showed trans-phosphines, cis-chloro ligands and a cis arrangement of a 4-electron donor imido ligand [W–N 1.763(6) Å] and a 2-electron donor alkyne [W–C 2.131(6) and 2.111(7) Å]. The compound Me3SiNHCHMe2 added to [{WCl4(PhC2Ph)}2] followed by dmbipy gave [WCl2(NCHMe2)(PhC2Ph)(dmbipy)] 8 (δ 163.16), Me3SiNHCH2Me and dmbipy formed cis- and trans-dichloro complexes [WCl2(NCH2Me)(PhC2Ph)(dmbipy)] 9 (δ 152.76 and 159.03) and 10 (δ 163.31) respectively. A crystal structure of determination 10 showed W–C bond lengths [2.085(8) Å] somewhat shorter than in 6, consistent with the increase in alkyne π⊥ donation for 10 indicated by δ. The compound Me3SiNHC6H3Pri2-2,6 and [{WCl4(PhC2Ph)}2] gave [{WCl2(NC6H3Pri2-2,6)(PhC2Ph)(NH2C6H3Pri2-2,6)}x] 11 (δ 166.51) which with dmbipy gave cis-dichloro [WCl2(NC6H3Pri2-2,6)(PhC2Ph)(dmbipy)] 12 (δ 167.50). Other complexes prepared were [WCl2(NC6H3Me2-2,6)(PhC2Ph)(dmbipy)] 13 (δ 167.26), [WCl2(NC6H3Pri2-2,6)(PhC2Ph)(py)2] 14 (δ 158.78) and [WCl2(NC6H3Pri2-2,6)(PhC2Ph)(PMe3)2] 15 (δ 154.40). The compound Me3SiNHC6H3Pri2 –2,6 and [NEt4][WCl5(PhC2Ph)] gave [NEt4][WCl4(NHC6H3Pri2-2,6)(PhC2Ph)] 16 where δ (167.40) indicates an amido ligand allows conversion of the alkyne into a 2-electron donor.