Photosubstitution Reactions of M(CO)₄(1,10-phenanthroline) (M = Mo, W). Influence of Entering Ligand, Irradiation Wavelength, and Pressure

Abstract

The influence of the entering nucleophile, irradiation wavelength, and pressure on the quantum yield for the photosubstitution of M(CO) 4 phen (M ) Mo, W) to produce M(CO) 3 -(L)phen (L ) PMe 3 , PPh 3 ) was investigated in toluene at 298 K. From the pressure dependence of the quantum yield apparent volumes of activation could be determined as a function of irradiation wavelength. These could be analyzed in terms of contributions arising from dissociative ligand field excitation and associative metal-to-ligand charge transfer excitation. The influence of steric hindrance on the entering ligand (PPh 3 > PEt 3 > PMe 3 ) controls the contribution of the associative charge-transfer photosubstitution reaction. An overall mechanistic picture is presented and discussed in reference to available literature data.

Light-Induced Insertion of a CO Ligand into an Os−N Bond of the Clusters Os3(CO)10(L), Where L Represents a Potentially Terdentate N,N‘-Chelating α-Diimine

“…Increasing the pressure from 0.1 to 150 MPa resulted in a small decrease of Φ 5 from 0.0820 (0.1 MPa) to 0.0757 (50 MPa), to 0.0714 (100 MPa), and 0.0710 (150 MPa). From these data the apparent volume of activation Δ V ‡ is obtained from the slope of the linear plot of ln[Φ/(1 − Φ)] vs pressure. ,− Values derived from such plots are preferred over those obtained from ln Φ vs pressure since they represent the difference between the volume of activation of the reaction and that of the nonradiative excited-state decay . The resulting value of Δ V ⧧ = +2.6 ± 0.6 cm 3 mol -1 is small, and mainly due to this fact the correlation coefficient is only 0.857.…”

Photochemistry of (η6-arene)Mo(CO)3 and the Role of Alkane Solvents in Modifying the Reactions of Coordinatively Unsaturated Metal Carbonyl Fragments

“…Until recently it has been assumed that CO loss occurs via a ligand field (LF) excited state; however, recent calculations on Cr(CO) 6 indicate that CO loss follows MLCT excitation . Evidence has also been presented which indicates that excited states resulting from MLCT excitation can undergo ligand exchange by associative mechanisms, whereas usually LF excited states react by way of dissociative processes . While it may be possible that such an explanation may account for the variation in quantum yield for CO loss in the (η 6 -arene)Mo(CO) 3 system, we believe that a more likely explanation for this observation is that two excited states, each with its own resultant photochemistry, are accessible for these systems similar to that observed for (η 6 -pyridine)Cr(CO) 3 .…”

Photochemistry of (η3-allyl)Ru(CO)3X Precursors for Photoassisted Chemical Vapor Deposition

“…However, there are also reports that suggest photosubstitution occurring directly from an MLCT state. Many of the reports indicate the photosubstitution occurring via associative substitution, − but there are also a few suggesting a dissociative interchange pathway. − …”