Formation of carboalkoxyiridium complexes by carbonylation of alkoxyiridium complexes and the crystal structure of trans-PhOIr(CO)(PPh3)2

Reactivity of Platinum−Oxygen Bonds: Kinetic and Mechanistic Studies of the Carbonylation of Platinum Aryloxide Complexes and the Formation of (Aryloxy)carbonyls

“…When the carbonylation is followed by 31 P{ 1 H} NMR, starting material is seen to cleanly convert to product; no other products or intermediates are seen, Figure . The IR spectra of compounds 3a , b , d show (aryloxy)carbonyl ν(CO) bands at 1677, 1655, and 1673 cm -1 , respectively, consistent with published spectra of other alkoxycarbonyls. ,,

2 Overlaid 31 P{ 1 H} spectra showing the disappearance of resonances corresponding to the aryloxide 2b and the appearance of the (aryloxy)carbonyl 3b .

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“… Atwood et al . found that nucleophilic addition of aryloxide to the coordinated carbon monoxide ligands of [Ir(CO) 2 (PPh 3 ) 2 ] + occurs during the reaction of Ir(CO)(PPh 3 ) 2 (OR) (R = Me, Ph) with carbon monoxide . Spectroscopic observation of the Ir(CO) 3 (PPh 3 ) 2 + intermediate in quantities dependent on phenoxide basicity supported this conclusion.…”

“…We report synthetic and mechanistic studies of platinum aryloxy and (aryloxy)carbonyl complexes. The chemistry of late transition metal aryloxides was once considered to be limited by the incompatibility of the “hard” basic ligands and “soft” metal centers. − In the wake of the earlier development of metal alkyl chemistry, there now exists a growing body of research on such complexes. , While a significant number of examples of late transition metal alkoxy complexes now exist in the literature, − the chemistry of late transition metal aryloxy complexes has been slower to develop. ,,,,,− Bercaw and Bryndza et al have shown that homolytic Pt−OR bond energies in alkoxy complexes are comparable to the Pt−C (sp 3 ) bond energies of the alkyl complexes . Compared to the alkoxy complexes, the chemistry of late transition metal aryloxy complexes is expected to reflect a weaker M−O bond, inasmuch as the homolytic and heterolytic bond strengths for aryloxide complexes are expected to be lower.…”

(silox)3RePMe3 (silox = tBu3SiO) is carbonylated to the double insertion product (silox)(Me3P){cis-(CO)2}Re{ trans-(CO2SitBu3)2 }

“…3 During the course of carbonylating a rhenium siloxide derivative, evidence of two formal CO insertions into Re-OSi t Bu 3 bonds was obtained. The insertion of CO into any metal-heteroatom bond is unusual, and the modest number of L n MCO 2 R isolated, [4][5][6][7][8][9][10] observed, 11 or inferred 12,13 from carbonylation reactions are mostly late transition metal compounds; [4][5][6][7][8][9][10][11] Since the J PC 100 Hz could be assigned to a large trans-P-Re- 13 CO coupling, a CO insertion to form a siloxy-acyl ligand, CO 2 Si t Bu 3 , was considered. An X-ray structural study of (silox)(Me 3 P){cis-(CO) 2 }Re{trans-(CO 2 Si t Bu 3 ) 2 } 5 corroborated this possibility, and proved fully consistent with the spectral data.…”

“…Consistent with the thermodynamic reasoning is the observation of H(silox) loss from (silox) 3 RePMe 3 2 upon hydrogenation. The mechanism of CO insertion, whether internal [4][5][6][7] or external 9,11 [i.e. L n (silox)Re + CO ?…”