Photoreactions of group 6 metal carbonyls with olefins

Abstract

Abstract

π-Complexes of Chromium, Molybdenum and Tungsten, Excluding those of Cyclopentadienyls and Arenes

“…The poor stability of d.s-[Cr(CO) 4 (r| 2 -C 2 H 4 ) 2 ] has been corroborated via a gas-phase synthesis 3 involving a pulsed UV eximer laser beam; interestingly no fra«s-[Cr(CO) 4 (r| 2 -C 2 H 4 ) 2 ] was observed in this latter synthesis and it is probable that CO dissociation fro m [Cr(CO) 5 (r| 2 -C 2 H 4 )] occurs preferentially cis to ethene leading to the formation of c*s-[Cr(CO) 4 (r| 2 -C 2 H 4 ) 2 ], which undergoes a subsequent, photochemically induced cis-trans isomerization. 4 Infrared and Raman spectroscopic studies on trans-\M(CO\(v\ -C 2 H 4 ) 2 ] (M = Mo or W) in hexane or liquid xenon suggest a D 2 r f symmetry with the ethene ligands in a trans -orthogonal orientation; 5 the stability o f this conformation has been rationalized in terms of the efficiency of metal to alkene (n*) back donation. 4 Photolysis of fra/w-[M(CO) 4 (rj 2 -C 2 H 4 ) 2 ] (M = W) in liquid xenon, doped with H 2 , affords the nonclassical dihydrogen complexes mer-[W(CO) 3 (r| 2 -H 2 )(r| 2 -C 2 H 4 ) 2 ] and CW-[W(CO) 4 (T| 2 -H 2 )(T| 2 -C 2 H 4 )]; analogous, but less stable, complexes are probably formed where M = Cr or Mo.…”

“…4 Infrared and Raman spectroscopic studies on trans-\M(CO\(v\ -C 2 H 4 ) 2 ] (M = Mo or W) in hexane or liquid xenon suggest a D 2 r f symmetry with the ethene ligands in a trans -orthogonal orientation; 5 the stability o f this conformation has been rationalized in terms of the efficiency of metal to alkene (n*) back donation. 4 Photolysis of fra/w-[M(CO) 4 (rj 2 -C 2 H 4 ) 2 ] (M = W) in liquid xenon, doped with H 2 , affords the nonclassical dihydrogen complexes mer-[W(CO) 3 (r| 2 -H 2 )(r| 2 -C 2 H 4 ) 2 ] and CW-[W(CO) 4 (T| 2 -H 2 )(T| 2 -C 2 H 4 )]; analogous, but less stable, complexes are probably formed where M = Cr or Mo. 6 The photochemical generation and reactivity o f the mixed diene-alkene complexes [M(CO) 3 (r| 2 -alkene)(r| 4 -nbd)] (M = Cr, Mo or W) is discussed in Section 6.4.2.…”

“…Room-temperature photolysis of [Cr(CO) 6 ] with cis -cyclooctene (cis-coe) affords isolable [Cr(CO) 5 (r| 2 -c/ 1 y-coe)] and correspondingly, with trans-coe, [Cr(CO) 5 (r| 2 -tam.s-coe)] followed by trans-[Cr(CO) 4 (T| 2 -fran.s-coe) 2 ]. 7 Time-resolved photoacoustic calorimetry studies reveal that the chromium-alkene bond strength in [Cr(CO) 5 (r\ 2 -trans-coe)] exceeds that o f the corresponding cis complex by ca.…”

“…The complexes [WC1 2 (PR 3 ) 4 ] (PR 3 = PMe 3 , PMe 2 Ph or PMePh 2 ) react with ethene to give c*VranHWCl 2 (PR 3 ) 2 (r| 2 -C 2 H 4 ) 2 ] 39 and reaction of [WCl 2 (O)(PMePh 2 ) 3 ] with CH 2 =CHR (R = H, Me or CH=CH 2 ) yields (4) in which the cis arrangement o f oxo and alkene ligands facilitates significant tungsten-alkene 7 t * interaction. Analogous imido and sulfido complexes [ W C 1 2 ( E ) ( P R 3 ) 2 ( T | 2 -alkene)] (PR 3 = PMe 3 or PMePh 2 ; alkene = ethene, propene, etc.…”

“…The tetrafluoroborate complex [Mo(CO) 3 4 ] via facile displacement of BF 4 " from the metal coordination sphere 45 and treatment o f [Mo(CO) 2 (t| 3 -C 3 H 5 )Cp] with HBF 4 affords [Mo(CO) 2 (FBF 3 )(Ti 2 -CH 2 =CHMe)Cp] which is a source o f the 14-electron fragment Mo(CO) 2 Cp + via displacement o f both BF 4 " and propene ligands. 46 Chelate phosphine derivatives [Mo(CO)(P-P)(ri 2 -RHC=CH 2 )Cp] + [P-P = dmpe, dppe or (MeO) 2 PCH 2 CH 2 P(OMe) 2 ; R = H, Ph, CO 2 Me, etc.]…”