Competition between Steric and Electronic Control of Structure in Ru(CO)₂L₂L‘ Complexes

Abstract

Magnesium reduction of RuCl2(CO)2L2 in the presence of equimolar L in THF gives Ru(CO)2L3 (L = PPh3 (1), PMePh2 (2), PEt3 (3), P i Pr2Me (4)). The corresponding reduction of RuCl2(CO)2(PEt3)2 in the presence of equimolar L‘ (L‘ = P(2-furyl)3 (5) or AsPh3 (6)) gives Ru(CO)2(PEt3)2L‘ but gives a mixture of Ru(CO)2(PEt3)3 - n L n (n = 0−3) species when L‘ = PPh3. Comparisons show that 3 or 5 reacts slowly with L‘‘ = (H)2, CO, or PhC⋮CPh to form Ru(CO)2L‘‘(PEt3)2 and free PEt3 or P(2-furyl)3 but rapidly with 4 or 6 to give the analogous products. The reaction of PhC⋮CPh with Ru(CO)2(PEt3)2L‘ is faster for L‘ = PEt3 than for P(2-furyl)3. All of these reactions are proposed to take place by preliminary ligand loss of L‘, this being slower for 3 and 5 than for 1, 4, and 6. Reaction of O2 with complexes containing the readily dissociated L‘ species gives simply Ru(η2-O2)(CO)2L2, but for Ru(CO)2(PEt3)3, this is accompanied by an apparent bimolecular electron transfer involving the intact complex to give Ru(CO)(CO3)(PEt3)3. X-ray structure determinations of Ru(CO)2(PEt3)3 (bis equatorial CO in trigonal bipyramid (TBP)), Ru(CO)2(P i Pr2Me)3 (two isomers: bis axial CO in TBP and also square pyramidal), and Ru(η2-PhCCPh)(CO)2(PEt3)2 (cis carbonyls and trans phosphines) are reported. It is shown that all of the Ru(CO)2L3 species exist in solution as two isomers in rapid equilibrium. Ab initio MP2 calculations on the unhindered Ru(CO)2(PH3)3 model shows a preference for a trigonal bipyramidal structure with only a weak preference for CO to be at the equatorial site. It is shown that this pattern cannot be generalized to all π-acid ligands since ethylene is calculated to have a strong preference for an equatorial site in a TBP. Integrated quantum chemical and molecular mechanics calculations on Ru(CO)2(PEt3)3 and Ru(CO)2(P i Pr2Me)3 give structures in excellent agreement with the X-ray results and confirm that the geometry and relative energetic preference for the observed structural isomers is strongly influenced, or even dominated by, the steric effect of the phosphine ligands.

Nano-palladium is a cellular catalyst for in vivo chemistry

“…1d). Some evidence suggests a higher affinity of TFP for in situ Pd(0) formation compared to triphenylphosphine19, which may be attributed to π-back bonding, as has been observed with Ru(0) and TFP20. Owing to low s-donicity, TFP readily dissociates from Pd(II) species, as shown by direct equilibration experiments21.…”

Iron(0) and ruthenium(0) complexes with tridentate phosphonite ligands and their potential for ketene formation from methyl iodide, CO and a base

“…Synthetic access to them involve either direct substitution on zerovalent ruthenium carbonyl complexes [45] or reduction of ruthenium(II) precursors in the presence of carbon monoxide [44,46,47]. The complexes 1-4 were prepared in good yields from the thermal reaction of the corresponding tridentate phosphine ligand with Ru 3 (CO) 12 in refluxing toluene (Scheme 4).…”

π‐Accepting‐Pincer Rhodium Complexes: An Unusual Coordination Mode of PCP‐Type Systems

“…The first is that all of the orbitals are lower in energy in complex 3 d. The second is that the ef- Overall, the geometries of the d 8 ML 5 -type complexes are determined by the preference of the s-donating aryl ligand to occupy an axial, rather than equatorial, position [33,34] and by the steric demand of the large phosphines which dictates that they occupy the equatorial plane of the tbp complex. [33] Summary A novel p-accepting PCP ligand and its rhodium complexes were synthesized. The coordination chemistry of this system differs significantly from that of other pincer-type ligands.…”