Abstract

98 Organometallics 1988, 7, [98][99][100][101][102][103][104][105] portant difference in chemical reactivity between Fe-(TMM)L3 complexes (L = PR3 (3) and L = CO): a oneelectron transfer easily occurs from 3 on attempts of alkylation and the resulting 17-electron intermediate is stabilized by the basic phosphines L, whereas Fe-(TMM)(CO), is the site of electrophilic substitutions,15 but its one-electron abstraction is difficult to perform and immediately undergoes decomposition, presumably via initial cleavage of an Fe-CO bond. This illustrates the deciding role of the nature of the ligands to modulate the behavior of complexes within the same family. Cyclic voltammetry of 6a-c showed a reversible oneelectron oxidation at negative potential corresponding to the formation of Fe(o-xylylene)L,+ (69, and an irreversible wave between 0.50 and 0.70 V was observed Conclusion Our results present an easy access to electron-rich (q4-hydrocarbon)iron complexes via FeC12(PR3)n intermediates, magnesium, and halogenated substrates. This method avoids the preliminary preparation of unstable Grignard reagents and should offer a potential for organometallic syntheses. The nature and the number of ancillary PR3 groups play a determining role for the reactivity of FeC12(PR3) with o-BrMgCH2C6H4CH3, which leads to either a C-H activation or a C-C coupling reaction. The studied Fe(q4-TMM)L3 and Fe(q4-o-xylylene)L3 complexes show at the same time a high tendency to give an electron transfer and an unexpected stability of the resulting paramagnetic species. These two characteristics, which are indicative of the electron-rich nature of the complexes, appear to be modulated by the electron-donor capability of the phosphorus groups and also by the type of interaction between the hydrocarbon ligand and the' metal. Acknowledgment. We are grateful to C. Mountassir and Dr. S. Sinbandhit for helpful assistance and discussions. Registry No. la, 55853-16-2; lb, 95911-92-5; Id, 55059-43-3; 2,1871-57-4; 3a, 95911-86-7; 3a+(CF3SOf), 95911-88-9; 3a+(N0<), 111409-15-5; 3c+(CF3S03-), 111409-17-7; 4a, 612-12-4; 5,56812-61-4; 6a, 111409-13-3; 6a+, 111409-14-4; 6b, 95911-91-4; 6d, 95911-89-0; 7,952-80-7; 8b, 111409-18-8; 9b, 110074-88-9; MeC-(CH2PMe&, 77609-83-7 The bonding and energetics in the C13MoC3H3 metallacyclobutadiene are contrasted with those in the metallatetrahedrane. The complexes are found to be within 20 kcal/mol of one another, with the metallatetrahedrane being the lower in energy. The Mo-C bonds are essentially covalent in both structures, and the metallacyclobutadiene posseseefl resonance stabilization. Charge distribution in the carbon fragments reveals no cyclopropenium character in the C3H3 ring of the metallatetrahedrane. Bonding, energetics, and charge distributions are all discussed with an emphasis on structure and reactivity.