Synthesis, Redox Chemistry, and Electronic Structure of the Alkynyl Cyclopentadienyl Molybdenum Complexes [Mo(C≡CR)(CO)(L₂)Cp′]ⁿ⁺ (n = 0 or 1; R = Ph or C₆H₄-4-Me, L₂ = Ph₂PCH₂CH₂PPh₂ or 2PMe₃, Cp′ = Cp or Cp*)

Reactions of (mesityl)n(methyl)2−nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex

“…Complex 11b has a four-legged piano stool structure with Cp*, two CO, PMe 3 and SiMes(Me)(OSiMe 3 ) ligands. The distances of the Mo–Si1 (2.6241(12) Å) and Mo–P (2.4313(10) Å) bonds were within the ranges of those reported for Cp*Mo(SiR 3 )(CO) 2 L (2.60–2.65 Å) 13 b , d ,18,24 and Cp*Mo(PMe 3 )(CO) 2 X (2.43–2.46 Å) 25 complexes.…”

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

“…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. [198] In the case of the trans system, the four-legged piano stool structure favours π-bonding interactions between the metal (d yz , d xz ) and the e 1 orbitals of the Cp ligand, whereas strong backbonding interactions between the carbonyl ligand and the remaining d orbital of π-type symmetry (d xy ) leads to d z character in the HOMO in this case. Consequently, trans-[Mo(CϵCR)(CO)(PMe 3 ) 2 CpЈ] complexes display similar metal-localised redox chemistry as the {Mo(CϵCR)-(dppe)(η 7 -C 7 H 7 )} systems, albeit for subtly different reasons.…”

“…Electronic structure calculations have been used to rationalise some of the more recent observations concerning the redox non-innocent character of σ-alkynyl and polyynyl ligands, particularly for complexes based on piano-stool fragments [M(L 2 )CpЈ] [M = Fe, L 2 = (dppe), CpЈ = Cp*; [13,14,17] M = Ru, L 2 = (PPh 3 ) 2 , dppe, CpЈ = Cp, Cp*], [10,18,32,128,153] [Mo(CO)L 2 CpЈ] [L 2 = (PMe 3 ) 2 , dppe; CpЈ = Cp, Cp*], [198] [M(dppe)(η 7 -C 7 H 7 )] [M = Mo, [20,21] W [19] ] and the octahedral moiety trans-[RuCl(dppe) 2 ]. [12,32] Many aspects of the computational rationalisation of ligand non-innocence have recently been reviewed by Costuas and Rigaut, [34] and so only key points will be emphasised here.…”

“…The lowering of symmetry from pseudo-C 4v towards C 2v permits a significant degree of rehybridisation of d z 2 and d x 2 -y 2, which hampers a simple description, but the key feature is the stabilisation of the resulting "on-axis" components by interaction with the carbonyl and alkynyl ligands. The consequence of greater alkynyl character in supporting the unpaired electron on oxidation is evidenced not only by computational studies of the precursor closed-shell derivatives (trans-[Mo(CϵCPh)(CO)(PH 3 [198] …”