MATRIX PHOTOCHEMISTRY OF MN-2(CO)(10) - REVERSIBLE FORMATION OF MN-2(CO)(8) FROM MN-2(CO)(8)(MU-ETA(1)ETA(2)-CO)

The CO-loss photochemistry of Mn-2(CO)(10) (1) has been investigated using frozen-matrix photochemical techniques. A solution of 1 (0.6 mM) in neat 3-methylpentane is cooled to 96 K to form a frozen matrix. Initial irradiation of the matrix with broad-band light from a medium-pressure Hg lamp produces the known single-CO-loss product Mn-2(CO)(8)(mu-eta(1):eta(2)CO) (3). Continued irradiation leads to additional loss of CO and the formation of new IR bands. When thermal back-reactions in the matrix at 96 K are monitored, two additional products are identified. One is Mn-2(CO)(8) (8), a double-CO-loss product from 1 that has only terminal CO ligands and may possess a Mn-Mn triple bond. The other product is an isomer of 3, Mn-2(CO)9' (9), which likely has a semibridging CO (nu(CO) 1728 cm(-1)). Under thermal conditions at 96 K, 8 and 9 reversibly reconvert to 3.