Multisite Magnetization Transfer Studies of Metal\nMigration in (η³-C₇H₇)Re(CO)₄, (η³-C₇H₇)Os(CO)₃SnPh₃,\n(η³-C₇H₇)Re(CO)₃PMe₃, (η⁵-C₇H₇)Re(CO)₃,\n(η⁵-C₇H₇)Fe(CO)₂SnPh₃, (η⁵-C₇H₇)Os(CO)₂SnPh₃, and\n(η⁵-C₇H₇)Ru(CO)₂SnPh₃^†

Abstract

Multisite magnetization transfer (MMT) studies of metal migration around the C₇H₇ rings\nin (η³-C₇H₇)Re(CO)₄ (<b>1</b>), (η³-C₇H₇)Os(CO)₃SnPh₃ (<b>2</b>), (η³-C₇H₇)Re(CO)₃PMe₃ (<b>3</b>), (η⁵-C₇H₇)Re(CO)₃ (<b>4</b>), (η⁵-C₇H₇)Fe(CO)₂SnPh₃ (<b>5</b>), (η⁵-C₇H₇)Os(CO)₂SnPh₃ (<b>6</b>), and (η⁵-C₇H₇)Ru(CO)₂SnPh₃ (<b>7</b>) are reported. The possible presence of 1,2-, 1,3-, and/or 1,4-metal shifts in the\nring fluxionality was investigated in all compounds, and it was shown that both 1,2- and\n1,3-shifts occur concurrently in <b>5</b> and <b>6</b>, but that only 1,2-shifts occur in <b>1</b>, <b>2</b>, <b>3</b>, and <b>4</b>, and\nonly 1,3-shifts in <b>7</b>. Several of the compounds exist as mixtures of isomers, and the application\nof MMT was crucial in unraveling the fluxionality of one isomer in the presence of the other.\nThus, MMT experiments allowed the study of the rate of metal migration in the symmetric\nisomer of <b>2</b>, which occurs in the presence of more rapid exchange in the asymmetric isomer.\nThe symmetric isomer of <b>3</b> was found to exchange faster than the asymmetric isomer. MMT\nstudy of the exchange between symmetric and asymmetric isomers of <b>7</b> at low temperatures\nshowed that the two enantiomers of the asymmetric isomer exchange directly with the\nsymmetric isomer, but not with each other. MMT experiments allowed the study of metal\nmigration in <b>7</b> in the presence of the isomer interchange process. The rate constants and\nfree energies of activation for the metal shifts and for the isomer interchange are reported.\nIt was concluded that orbital symmetry considerations do not provide useful predictions\nabout the mechanisms of metal migration in compounds containing η¹-, η³-, or η⁵-C₇H₇ rings.