Synthesis of dicarbonyl and halogeno complexes of (η-pentamethyl-cyclopentadienyl)(nitrosyl)-molybdenum and -tungsten. Crystal structure of [{Mo(η5-C5Me5)(NO)Br(µ-Br)}2]

Abstract

Under appropriate conditions the reaction of [M(η⁵-C₅Me₅)(NO)(CO)₂][M = Mo, (1) or W, (2)] with X₂(X = Cl, Br, or l) gives [{M(η⁵-C₅Me₅)(NO)X₂}_n][M = Mo, (3a)–(3c); or W, (4a)–(4c); n= 1 or 2]. When M = W and X = Cl the new carbonylnitrosyl compound [W(η⁵-C₅Me₅)(NO)-Cl₂(CO)](5) has been isolated and characterized; (5) is proposed to be an intermediate in the preparation of (4a) from (2). The compound (3b) or (4b) reacts with mono- or bi-dentate phosphines giving [M(η⁵-C₅Me₅)(NO)Br₂L][L = PPh₃, M = Mo, (6b); or W, (7); L = OPPh₃, M = Mo, (8); or W, (9)] or [Mo(η⁵-C₅Me₅)(NO)Br(L–L)][Mo(η⁵-C₅Me₅)(NO)Br₃][L–L = Ph₂PCH₂PPh₂(dppm), (10); or Ph₂PCH₂CH₂PPh₂(dppe), (11)]. Complex (11) is in equilibrium with an isomer [Mo₂(η⁵-C₅Me₅)₂(NO)₂Br₄(dppe)](12). X-Ray structure analysis of [{Mo(η⁵-C₅Me₅)(NO)-Br(µ-Br)}₂](3b) shows space group C2/c with a= 15.102(4), b= 8.403(6), c= 21.498(10)Å, β= 98.69(2)°, and Z= 4; R= 0.063 and R′= 0.055, based on 2 688 observed reflections. The molecule is dimeric with two bridging bromo atoms, in contrast with the monomeric nature of the recently reported structure of the parent (4c).