Synthesis and Photochemistry of Alkylated Photochromic Manganese Complex Precursors

Two alkylated cymantrene derivatives, one disubstituted Mn[η5-C5H3(β-{CH2}6CH3)CH2CO(C5H4N)](CO)3, (4) and one monosubstitutedMn[η5-C5H4CH({CH2}6CH3)CO(C5H4N)](CO)3 (10) have been synthesized and characterized spectroscopically. UV photolysis of 4 and 10 in n-heptane resulted in the formation of chelatesMn[η1:η5-C5H3(β-{CH2}6CH3)CH2CO(2-py- κ-N)](CO)2 (14) andMn[η1:η5-C5H4CH({CH2}6CH3)CO(2-py- κ-N)](CO)2 (16), respectively. Both resultant purple chelates exhibit an N-chelate spectroscopically based on previous analysis ofMn[η1:η5-C5H4CH2CO(2-py- κ-N)](CO)2 (3). TRIR experiments with UV photolyzing (4) in n-heptane yielded a mixture ofMn[η1:η5-C5H3(β-{CH2}6CH3)CH2(CO- κ-O)(2-py)](CO)2 (13) and 14 (O- and N-chelate, respectively) with a greater abundance of 13 within the ns timescale. The opposite is noticed within the ns timescale when 10 is UV-photolyzed in n-heptane (greater abundance of 16 than Mn[η1:η5-C5H4CH({CH2}6CH3)(CO- κ-O)(2-py)](CO)2 15). The rate of conversion of O-chelate 13 to N-chelate 14 (k = 1.6 x 10-2 s-1) is slower than the conversion of O-chelate 15 to 16 (k = 1.2 x 10-3s-1)