Molybdenum-based alkyne–isocyanide coupling reactions: synthesis of a reactive diiminometallacyclopentene complex

The d3/d2alkyne complexes [MX2(η-RCCR)Tp′]z(X = halide, z = 0 and 1+): final links in a d6–d2redox family tree

“…For example, [FeF(dppe)(h-C 5 Me 5 )][PF 6 ] is formed in the oxidation of [Fe(dppe)(h-C 5 Me 5 )][ PF 6 ] with [Fe(h-C 5 H 5 ) 2 ][PF 6 ], 5 and [MoF(CNxylyl) 4 (h-C 5 Me 5 )][BF 4 ] 2 results from the reaction of Ag [BF 4 ] with [Mo(CNxylyl) 4 (h-C 5 Me 5 )][ BF 4 ]. 6 A more rational synthesis of [WF 2 (h-PhC∫CPh)Tp¢] + was then developed using N-fluoropyridinium tetrafluoroborate, [Fpy][BF 4 ], as both the strong oxidant and a potential source of the second fluoride ligand. Thus, treatment of [WF(CO)(h-PhC∫CPh)Tp¢] with [Fpy][BF 4 ] in CH 2 Cl 2 led to slow loss of the IR carbonyl band and formation of a red-orange solution which was filtered through Celite and then evaporated to dryness in vacuo.…”

“…The discovery of the one-electron oxidation of [Cr(CO) 2 (h-RC∫CR)(h 6 -arene)] and the one-electron reduction of [M(CO) 2 (h-RC∫CR)Tp¢] + , and the consequent structural characterisation of the redox pairs [Cr(CO) 2 (h-PhC∫CPh)(h 6 -C 6 Me 5 H)] z (z = 0, d 6 and 1+, d 5 ) 1 and [Mo(CO) 2 (h-PhC∫CPh)Tp¢] z (z = 0, d 5 and 1+, d 4 ), 2 enabled us to show that stepwise electron removal from a (formally) d 6 complex converted the coordinated alkyne from a two-to a three-to a four-electron donor. Halide substitution of one carbonyl ligand of [M(CO) 2 (h-RC∫CR)Tp¢] + then gave [MX(CO)(h-RC∫CR)Tp¢] (M = Mo or W, X = halide) which was oxidised to the isolable d 3 cation [MX(CO)(h-RC∫CR)Tp¢] + , again structurally characterised (M = W, X = Cl or Br).…”

“…This paper describes the full characterisation of [MX 1 X 2 (h-RC∫CR)Tp¢] + (R = Me, M = W, X 1 = X 2 = F; R = Ph, M = Mo, X 1 = X 2 = F; M = W, X 1 = X 2 = F or Cl; X 1 = F, X 2 = Cl) and the one-electron reduction to the neutral analogues [MX 1 X 2 (h-RC∫CR)Tp¢], completing a redox family tree in which well defined d 6 and d 2 alkyne complexes are formally connected by a series of ligand substitution and one-electron transfer reactions.…”

Photochemistry of a Puckered Ferracyclobutadiene in Liquid Solution Studied by Time‐Resolved Fourier‐Transform Infrared Spectroscopy

“…Class B MCBDs display weaker π bonding between the metal and the C α atoms, and no interaction between the metal and the C β atom 8c,d. These MBCDs contain mostly a six‐coordinate metal center in a lower oxidation state 3a. 4–7 Remarkably, MCBDs are either planar or puckered metallacycles, which may display extensive or only little π‐electron delocalization.…”

Chemistry of Metallacyclobutadienes

“…Similarly, treatment of ferracyclobutinimine 24 with Et 3 OBF 4 produced ferracyclobutadiene 25 . In a related transformation, treatment of the diiminomolybdenacyclopentene 26 with HBF 4 produced the molybdenacyclobutadiene 27 . The reaction may proceed by initial protonation of an imine nitrogen of the diiminometallacyclopentene complex followed by a deinsertion of xylyl isocyanide.…”