Ligand-centred coupling of the alkynyl radical cations [Mo(CCR)(Ph2PCH2CH2PPh2)(η-C7H7)]+ (R = Ph or Bun: crystal structure of the dimeric product [Mo2(Ph2PCH2CH2PPh2)2(η-C7H7)2(μ-C4R2)][PF6]2 (R = Ph)

Oxidative Dimerization of Arylalkynyl–Ruthenium Complexes

“…We note that previous examples of coupling at C β have been found with [M(CCH)(dppe)Cp*] þ (M = Fe, Ru) 3,4 and with [Mo(CCPh)(dppe)(η-C 7 H 7 )] þ . 17 In the present examples, where the new CÀC bond is formed between the electron-rich atoms C β and C para of the Ph group, coupling appears to be directed by a combination of the high spin densities at C β and C para and steric factors which preclude coupling between both C β atoms. If the C para position is blocked, e.g., as in the p-tolylethynyl complex, then attack by C β proceeds at the Cp ring.…”

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

“…The sterically demanding analogue 19-tBu does not dimerise, but instead affords the cationic vinylidene 21 upon prolonged stirring. [113,114] The lack of dimerisation exhibited in the tertbutyl-functionalised derivative is logically attributable to steric hindrance at the C β atom of the alkynyl radical, whereas the slow reaction is a consequence of the significant d z 2 character of the β-LUSO) (lowest unoccupied spin orbital) in [Mo(CϵCC 6 H 5 )(dppe)(η 7 -C 7 H 7 )] + , which offers a poor symmetry match with the alkynyl π orbitals and thereby limits the concentration of spin density on the alkynyl moiety (see below). [20] Similar observations have been made for the series of complexes [Fe(CϵCR)(dppe)Cp*]; the CϵCH acetylide complex dimerises on low-temperature oxidation [112] whereas the tert-butyl, phenyl and a range of other substituted arylalkynyl complexes form stable, isolable radical cations.…”

“…Nevertheless, sufficient spin density is associated with the alkynyl ligand in [M(CϵCR)(dppe)(η 7 -C 7 H 7 )] + systems to give rise to hyperfine couplings with the alkynyl substituent R in both alkynyl [19][20][21]201] and polyynyl [155] systems, as well as C β -C β coupling processes in the least sterically encumbered derivatives. [113,138,155] In the case of four-legged piano-stool structures such as trans-[Mo(CϵCR)(CO)(PMe 3 ) 2 CpЈ] and cis-[Mo(CϵCR)-(CO)(dppe)CpЈ] (CpЈ = Cp, Cp*; Figure 5), there are important differences in the nature of the frontier orbitals brought about by the position of the carbonyl ligand and the requirement of the system to maximise back-bonding and minimise the overall energy. These orbital characteristics are preserved on one-electron oxidation and account for the different degree to which the metal centre and alkynyl ligand support the unpaired electron.…”

Open-shell organometallics: reactivity at the ligand

“…Alkynyl complexes of Mo(Ph 2 PCH 2 CH 2 PPh 2 )(C 7 H 7 ), for example, tend to dimerize forming dinuclear bis-vinylidene complexes but form a mononuclear vinylidene complex through H-atom abstraction when the steric bulk of the alkynyl ligand hampers the dimerization process. 54 Similar results were obtained for diynyl molybdenum radicals (Fig. 21).…”