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.