85362-16-9Relevant academic research and scientific papers
Photochemistry of organometallic halide complexes. Mechanisms for the formation of ionic products
Pan, Xiong,Philbin, Cecelia E.,Castellani, Michael P.,Tyler, David R.
, p. 671 - 676 (2008/10/08)
The photochemical reactions of the Mn(CO)5X (X = Cl, Br, I), CpMo(CO)3X (X = Cl, I), and CpFe(CO)2I complexes with various ligands were investigated with an emphasis on determining how ionic products form in these reactions. Two pathways account for the formation of ionic products: (1) M-X heterolysis and (2) metal-metal-bonded dimer formation followed by subsequent disproportionation. The metal-metal-bonded dimer may form via a secondary photolysis of a M-CO-loss photoproduct, via M-X heterolysis, or via a minor M-X homolysis pathway, followed by coupling of two metal radicals. CpMo(CO)3X reacts photochemically with a variety of ligands to give substitution products, but ionic products form only with pyridine and DMSO. With pyridine, the following sequence of reactions was found to yield ionic products: (1) CpMo(CO)3Cl →hν CpMo(CO)3 + Cl; (2) 2CpMo(CO)3 → Cp2Mo2(CO)6; (3) Cp2Mo2(CO)6 →hν CpMo(CO)3- + CpMo(CO)3py+. (Reaction 3 is the photochemical disproportionation of Cp2Mo2(CO)6 described previously by us.) The CpMo(CO)3X complexes are the only halides studied for which some M-X homolysis occurs; however, homolysis of the Mo-X bond is very inefficient: Φ = 9 × 10-4. For CpMo(CO)3X in DMSO, the only ionic product is CpMo(CO)2(DMSO)2+, formed by the following route: CpMo(CO)3Cl + DMSO →hν CpMo(CO)2(DMSO)Cl →hν CpMo(CO)2DMSO+ + Cl- → CpMo(CO)2(DMSO)2+. Ionic products form in the photochemical reactions of Mn(CO)5X complexes via the following route involving initial Mn-CO bond dissociation: Mn(CO)5X →hν Mn2(CO)8X2 →hν MnX2 + 3CO + 1/2 Mn2(CO)10. Photochemical disproportionation of the Mn2(CO)10 complex then occurs. Ionic products also form in the photochemical reactions of the CpFe(CO)2I complex via the intermediate formation of the metal-metal-bonded dimer, followed by disproportionation of this species. In this case, however, the dimer is formed by initial heterolysis of the Fe-I bond (CpFe(CO)2I →hν CpFe(CO)2+ + I-) followed by the sequence of reactions in Scheme II.
Low-Temperature Photochemistry of (η5-C5R5)Fe(CO)2Mn(CO)5 (R = H, Me): Substitution by P-Donor Ligands and Kinaetics of Thermal Fe-Mn Bond Homolysis
Pope, Keith R.,Wrighton, Mark S.
, p. 4545 - 4552 (2007/10/02)
Low-temperature irradiation of (η5 C5R5)Fe(CO)2Mn(CO)5 (R = H, Me) results in loss of CO as the only detectable photoprocess (Φapp for CO = 10-3 at 313 nm, and Φ313/Φ366 = 20 at 93 K) and yields a coordinatively unsaturated dinuclear photoproduct, (η5C5R5)FeMn(CO)6.It should be appreciated that CO loss and Mn-Fe bond cleavage are competitive processes with CO loss far more dominant at low temperature in a rigid glass.Warming of a glass containing (η5-C5R5)FeMn(CO)6 in the presence of PR3 (R = Ph, OPh) results in formation of (η5-C5R5)Fe(CO)2Mn(CO)4PR3.The substitution product could be generated by an independent route from irradiation of a room temperature solution of 5-C5R5)Fe(CO)2>2 and 2.Spectroscopic evidence, including IR, UV-vis, NMR, and MS, supports the conclusion that substitution of CO by PR3 in (η5-C5R5)Fe(CO)2Mn(CO)5 occurs exclusively on the Mn atom.It was further determined that Φdiss for (η5-C5H5)Fe(CO)2Mn(CO)5 at room temperature in the presence of P(OPh)3 in CCl4 is 0.89 +/- 0.08 and 0.89 +/- 0.1 at 313 and 366 nm, respectively, and Φapp for (η5-C5H5)Fe(CO)2Mn(CO)4P(OPh)3 is 0.26 +/- 0.03 and 0.29 +/- 0.04 at 313 and 366 nm, respectively, in the same solution.The products (η5-C5R5)Fe(CO)2Mn(CO)4PPh3 are labile with respect to Fe-Mn bond cleavage and a kinetic analysis yielded activation parameters for this thermal reaction ΔH = 106 +/- 6 and 84.3 +/- 4 kJ mol-1 for R = H, Me, respectively, and ΔS = 41.5 +/- 40 and -21.4 +/- 23 J mol-1 K-1 for R = H, Me, respectively.
