Synthesis, characterisation, and molecular and electronic structure of CpMoCl2(R1CCR2) (R1, R2 = Ph, Et, Me): a new class of half-sandwich 17-electron molybdenum(III) organometallics

Abstract

Addition of alkyne to [CpMoCl2]2 affords compounds CpMoCl2(η 2 -alkyne) (alkyne = EtC≡CMe, 1; EtC≡CEt, 2; PhC≡CMe, 3; PhC≡CPh, 4) in good yields. The compounds have been characterised by C,H analyses, IR, EPR and mass spectroscopies, magnetic susceptibility, and cyclic voltammetry. In addition, a single crystal X-ray diffraction analysis has been carried out for compound 4. The alkyne ligand adopts an almost parallel conformation relative to the Cp ring, essentially identical with that of previously reported Nb, Ta, and W analogues. Geometry optimisations on the CpMCl2(HC≡CH) (M = Nb, Mo) model compounds show that the total energy is nearly independent of the alkyne orientation. The SOMO for M = Mo is an essentially metal-based orbital with a slight Mo-Cl π* component, in agreement with the observed trends in M-Cl bond lengths on going from Group 5 to Group 6. The cyclic voltammetric behaviour of 1-4 is similar to the analogous diene complexes CpMoCl2(η 4diene). A reaction between 1-4 and excess alkyne takes place only for the dialkylsubstituted alkyne complexes under forcing conditions. Compound CpMoCl2(η 4 -C4Et4H), 5, has been isolated from the reaction between 2 and excess EtC≡CEt and crystallographically characterized. CNT-Mo-Cl(1) 112.6(2) C(9)-Mo-Cl(1) 137.51(7) CNT-Mo-Cl(2) 111.7(2) C(7)-Mo-Cl(1) 84.55(7) CNT-Mo-C(6) 106.5(2) C(6)-Mo-Cl(2) 140.61(8) CNT-Mo-C(9) 109.7(2) C(9)-Mo-Cl(2) 80.85(7) Cl(1)-Mo-Cl(2) 80.36(2) C(7)-C(6)-Mo 86.0(2) C(6)-Mo-C(9) 77.52(10) C(8)-C(9)-Mo 77.8(2) C(6)-Mo-C(7) 38.02(10) C(10)-C(6)-Mo 147.9(2) C(9)-Mo-C(7) 63.06(9) C(16)-C(9)-Mo 126.2(2) C(3)-Mo-C(7) 131.65(9) C(8)-C(9)-C(16) 122.9(2) C(6)-Mo-C(8) 65.26(9) C(7)-C(6)-C(10) 126.1(2) C(9)-Mo-C(8) 35.16(9) C(8)-C(7)-C(6) 115.2(2) C(7)-Mo-C(8) 34.11(9) C(7)-C(8)-C(9) 116.8(2) C(6)-Mo-Cl(1) 93.97(8)

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

“…Theoretical studies showed that the SOMO of [MoCl 2 (h-HC 2 H)(h-C 5 H 5 )] is also partly Mo-Cl p* in character. 12 The angle X(1)-W(1)-X(2) in the cations 1 + -4 + and 6 + is very similar to that of the isoelectronic d 2 complex [NbCl 2 (h-PhC∫CMe)Tp¢] (102 • ), whereas in the neutral species 2, 4, 7 and 8 that angle is narrower (90-97 • ). The obtuse angle in [NbCl 2 (h-PhC∫CMe)Tp¢] was ascribed 17 to the alleviation of a destabilising interaction between a filled d xz orbital on the metal and a linear combination of p p Cl orbitals.…”

“…The 'orthogonal' alkyne orientation differs from that in the cyclopentadienyl analogue [MoCl 2 (h-PhC∫CPh)(h-C 5 H 5 )] where the C∫C bond is more nearly parallel to the C 5 ring. 12 Theoretical studies on [NbCl 2 (h-RC∫CR)Tp¢], 16 with the orthogonal arrangement, 17 For the redox pairs [WX 2 (h-PhC∫CPh)Tp¢] z (z = 0 or 1+, X = F or Cl) Db increases on reduction, with the alkyne aligned more closely with bond X(2)-W(1), by 18.2 and 12.9 • for X = F and Cl respectively. This alkyne alignment is also observed in the neutral molybdenum complexes 7 and 8 (Db = 40.9 and 20.8 • respectively).…”

“…and [NbCl 2 (h-HC∫CH)(h-C 5 H 5 )] 12,18 and [MoCl 2 (h-HC∫CH)(h-C 5 H 5 )]12 (both with the alkyne parallel to the C 5 ring), suggested that such geometrical preferences result from steric rather than electronic effects.The precise orientation of the alkyne in [MX 1 X 2 (h-PhC∫CPh)Tp¢] z (z = 0 or 1+) depends on the electronic configuration of the metal centre. The dihedral angles b X(1) and b X(2) {formed by the C(16)-C(17) and X(1)-M(1) or X(2)-M(1) bonds respectively} of the cations [MX 2 (h-PhC∫CPh)Tp¢] + (X = F or Cl) are similar.…”

A reinvestigation of compound CpMo(PMe3)2(CH3)2: alkylation by single electron transfer and radical addition?

“…16 Compound CpMo( 4 -C 4 H 6 )(CH 3 ) 2 , as well as analogues with different diene and alkyl groups, displays a reversible reduction, while the first oxidation is completely irreversible even at 1000 V . s -1 and a second oxidation is not observed 19 (see Table 3).…”

The d2/d3 alkyne redox pair [WF2(PhCCPh)Tp′]z (z = +1 or 0): missing links in a ‘redox family tree’

“…We have recently reported the synthesis of three related redox pairs, namely [Cr(CO) 2 (h-PhC•CPh)(h-C 6 Me 6 )] z (z = 0, d 6 ; z = 1, d 5 ), [Mo(CO) 2 (h-PhC•CPh)TpA] z (z = 0, d 5 ; z = 1, d 4 5 formally by a sequence of steps involving one-electron oxidation followed by ligand substitution. Although not all members of this family tree have been identified for all of M, X and L there is sufficient evidence to suggest that the missing members may be chemically accessible.…”