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A major factor influencing Co-C bond stability both in B12 compounds and organocobalt BI2 models appears to be the coordination number. Five-coordinate complexes are unusually stable to Co-C bond thermolysis, but structurally characterized examples of five-coordinate organocobalt complexes are rare. None are known for cases where R is a bulky group, such as i-C3H7. We report two definitive examples of five-coordinate complexes of the type Co(saloph)R, where saloph = dianion of disalicylidene-o-phenylenediamine. The structure of one species (R = i-C,H7) permits the first assessment of the effects of R bulk on the structure and also provides insight into the structural basis for the thermal stability of the species of reduced coordination number. We have also characterized the third example of a six-coordinate organocobalt saloph compound.Specifically, the crystal and molecular structures of Co(saloph)-i-C,H7-1.5H20 (I), Co(saloph)CH,.0.5H20 (11), and pyCo(saloph)CH2CF3 (py = pyridine) (111) are described. Compounds I and I11 are pentacoordinate and hexacoordinate, respectively, while crystals of I1 are comprised of both pentacoordinate and dimeric molecules. Crystallographic details follow. I: C23H21C~N202-1.5H20, space group Pbcn, a = 26.075 ( 6 ) A, b = 9.617 (3) A, c = 16.109 (3) A, Dcalcd = 1.46 g cm-,, Z = 8, R = 0.057 for 5437 measured reflections. 11: C21H17CoN202~0.5H20, space group P i , a = 12.100 (8) A, b = 20.392 (9) A, c = 11.606 (8) A, LY = 53.3 (l)', p = 127.6 (I)', y = 121.7 (l)', Dcald = 1.50 g ~m -~, Z = 4, R = 0.041 for 7360 measured reflections. 111: C27H21CoN302F3-0.5H20.0.5C5H5N, space group P21/c, a = 14.255 (8) A, b = 19.318 (8) A, c = 19.434 (8) A, 0 = 93.7 (I)', Dcalcd = 1.45 g ~m -~, Z = 8, R = 0.055 for 13588 measured reflections. Several interestingfeatures emerge from these structures. First, the Co atom in I and I1 is displaced toward R. Second, the Co-C bond is shorter than in hexacoordinate compounds, but steric strain remains for i-C,H7 even in the pentacoordinate species. Third, in the unusual example of both a dimeric and monomeric molecule in the same crystal in compound 11, the monomeric form seems to be stabilized by the water of crystallization. This water is hydrogen-bonded to the saloph ligand and not coordinated to Co. Dynamic IH NMR measurements of 3,5-lut exchange in 3,5-lutCo(saloph)R (where 3,5-lut = 3,5-lutidine, R = CH2CN, CH2CF,, or CH,) reveal that the rate of exchange increases more rapidly with increasing electron donation by R in the series CH2CN to CH2CF, to CH3 than in other classes of BI2 compounds. The saloph ligand has recently been shown to exhibit a large structural cis influence and a large kinetic cis effect compared to the other classes of models. It was also recently recognized that the trans and cis influences are synergistic. Thus, the dynamic NMR measurements provide evidence that the cis and trans kinetic effects are also synergistic. When R = CH,, for example, exchange of the neutral axial ligand in saloph complexes is approximately 8 X 1O' O ti...

J. Am. Chem. Soc.sequence, the energy for ionization of the iron ion in these complexes is dramatically lowered, thus rendering more accessible the iron(1V) oxidation state. The d-orbital energy levels must be directly related to the inductive effect of the axial u-bonded group. This assumption is strengthened by the fact that half-wave potentials of +0.25 and +0.39 V are observed for (OEP)Fe(n-C4Hg) and (C I ,TPP) Fe(n-C4Hg), re~pectively,~~ compared to potentials of +0.48 V for oxidation of (OEP)Fe(C6Hs) and +0.61 V for oxidation of (TPP)Fe (C,H,).The half-wave potential of the second oxidation appears to be insensitive to the nature of the axial ligand. This electron transfer takes place at E,, = +1.43 V in CH2C12 or El,? = +1.52 V in DME, 0.1 M TBA(PF,), for (TPP)Fe(C6HS) while the oxidation half-wave potential for (TPP)FeX occurs at Ellz = +1.40 V in CH2CI2, 0.1 M TBA(C104) (where X stands for an anionic halide or p~eudohalide).~~ These observations suggest that the first oxidation of (P)Fe(C&) effectively occurs at the metal center.The electronic absorption spectra of the one-electron oxidized species obtained are in agreement with the above statement. For

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