PHOTOCHEMISTRY OF METAL-METAL BONDED COMPLEXES III. MLCT PHOTOLYSIS OF (CO)5MM'(CO)3(α-diimine) (M, M' = Mn, Re) IN 2-Me-THF AND THF AT 293 K; EVIDENCE OF PHOTOCATALYTIC FORMATION OF + - UPON PHOTOLYSIS IN THE PRESENCE OF P(n-Bu)3

Article abstract of DOI:10.1016/0022-328X(85)88053-0

Complexes of the type (CO)5MM'(CO)3(α-diimine) (M, M' = Mn, Re) were photolyzed in 2-Me-THF at 293 K in the absence and presence of PR3 by irradiation in the low energy M' -> α-diimine charge transfer band.In most cases the primary photoprocess appeared to be homolysis of the (M - M') metal-metal bond.In the absence of PR3 the radicals formed react eith each other to give M2(CO)10 and M'2(CO)6(α-diimine)2.It is shown that the stabilities of these M'2(CO)6(α-diimine)2 complexes depend on the α-diimine ligand used.In the presence of PR3 various reactions are observed, depending on the complex and the PR3 ligand used.Thus, photolysis of (CO)5MnRe(CO)3(α-diimine) in the presence of PPh3 or P(n-Bu)3 gives Mn2(CO)10 and a reaction product of Re2(CO)6(α-diimine)2.However, (CO)5MnMn(CO)3(α-diimine) in the presence of PPh3 gives Mn2(CO)8(PPh3)2 instead of Mn2(CO)10.A remarkable reaction is observed when a (CO)5MnMn(CO)3(α-diimine) complex is photolyzed in the presence of the basic phosphine P(n-Bu)3 the ionic compound ^{+ -} being formed as the result of electron transfer from the radical Mn(CO)3(α-diimine)(P(n-Bu)3) to Mn(CO)5 and (CO)5MnMn(CO)3(α-diimine).This reaction is a photocatalyzed chain reaction with Φ ca. 10.All these reactions involve initial homolysis of the metal-metal bond.Only in the case of (CO)5ReMn(CO)3(R-DAB) in the presence of PR3 was a carbonyl group of the Mn(CO)3(R-DAB) fragment photosubstituted.The mechanisms of the reactions are discussed.