Paramagnetic carbenemetal complexes. Part 1. Cationic chromium(I) complexes and the chemistry of their chromium(0) precursors and of related molybdenum(0) and Tungsten(0) complexes, especially with bulky carbene ligands C(OR′)R[R CH(SiMe3)2 or CH2SiMe3]

Abstract

Carbenemetal complexes having bulky alkyl substituents at C_carb., [M(CO)₅{C(OR′)R}][M = Cr, Mo, or W; R = CH₂CMe₃, CH₂SiMe₃, or CH(SiMe₃)₂; R′= Me, Et, or SiMe₃], are reported; a noteworthy feature is the good thermal stability of the molybdenum(0) complexes. Photolysis of [Cr(CO)₅L][L = C(OEt)CH(SiMe₃)₂ or [graphic omitted]Et (abbreviated as L^Et)] in the presence of P(OPh)₃, dmpe, or dppe yields fac-[Cr(CO)₃(L)L′₂][L′= P(OPh)₃ or L′₂= Me₂P(CH₂)₂PMe₂(dmpe) or Ph₂P(CH₂)₂PPh₂(dppe)]. Addition of Ag[BF₄] to the latter in CH₂Cl₂ affords [Cr(Co)₃(L)L′₂]⁺, characterised by e.s.r. spectroscopy. The dmpe complex with L = L^Et is stable at ambient temperature [unlike the other two chromium(I) analogues] and is well characterised, m.p. 95 °C, as is [Cr(CO)₃{C(OEt)CH(SiMe₃)₂}(dmpe)][BF₄]. The g_av factors for the 10 new chromium(I) salts are ca. 2.02 which suggests that significant unpaired spin is delocalised away from the metal, consistent with the low ⁵³Cr isotropic, hyperfine coupling constant (ca. 1.3 mT). Detailed i.r., ¹H and ¹³C n.m.r., and He(l) photoelectron spectroscopic, as well as mass spectrometric, data are described for the carbenemetal(0) complexes.