Reaction of free-base porphyrins (H2Por = octaethylporphyrin (OEP), meso-tetraphenylporphyrin (TPP), meso-tetra-p-tolylporphyrin (TTP), meso-tetrakis(4-tert-butylpheny1)porphyrin (TBPP), meso-tetrakis(3,4,5-tri-methoxypheny1)porphyrin (TMPP)) with 2 equivof MN(SiMe& ( M = Li, Na, K) in T H F or dimethoxyethane (DME) yields dimetal salts of empirical formula M z ( T H F )~P o~ and M2(DME)2Por, respectively. The lithium derivatives crystallize from donor solvents in the form of 1:l salts [Li(solv),] [Li(Por)] (solv = THF, n = 4; solv = DME, diacetone alcohol, n = 2). The crystallography determined structure of the TMPP derivative crystallized from acetone consists of a [Li(TMPP)]-anion and a [Li(diacetone alcohol)2]+ counterion. 'Li N M R spectroscopy and conductivity measurements suggest these ionic structures are retained in polar solvents; however, in relatively nonpolar solvents symmetrical ion-paired structures are observed. For the larger sodium ion, X-ray crystallography shows two Na(THF)2 moieties symmetrically bound to all four nitrogens, one on each face of the porphyrin ring. The structure of the pyridine complex K 2 ( p~r )~( o E P ) has also been determined; it is similar to the sodium salt but shows the solvent molecules positioned perpendicular to the porphyrin ring, presumably to maximize winteractions between neighboring molecules in the crystal. X-ray data are as follows: Li2(C6H1202)2 (TMPP): Pi with a = 12.420(2) A, b = 12.965(2) A, c = 13.998(2) A, CY = 66.29(2)', / 3 = 60.21(2)', y = 77.00(2)', V = 1790 A3, d,,,, = 1.23 g ~m -~, and 2 = 1. Na2-(THF)4(0EP): Pi with a = 9.801(3) A, b = 11.598(3) A, c = 12.106(2) A, (Y = 96.81(2)', j3 = 106.67(2)', y = 107.52(2)', V = 1225 A3, d,,, = 1.18 g ~m -~, and 2 = 1. K2(pyr)4(0EP): Pi with a = 10.102(4) A, b = 13.974(5) A, c = 19.029(4) A, a! = 89.88(2)', j3 = 76.78(2)', y = 72.90(2)', V = 2493 A', d,,~, = 1.24 g ~m -~, and Z = 2. help with the 'Li N M R experiments, the Department of Education for a fellowship (to C.G.H.), and the National Physical Sciences Consortium for a fellowship (to D.Y.D.). Note Added in Proof The interaction of dodecaphenylporphyrin with lithium iodide was recently reported to yield the corresponding porphyrin4ilithium salt. See: Tsuchiya, S . J . Chem. SOC., Chem. Commun. 1992, 1475.Supplementary Material Available: Tables of temperature factor expressions, positional parameters, intramolecular distances and angles, least-squares planes, and anisotropic thermal parameters (37 pages); listings of observed and calculated structure factors (85 pages). Ordering information is given on any current masthead page.

A new series of tantalum complexes incorporating bis(trimethylsilyl)benzamidinate ligands has been prepared and fully characterized; examples include species with alkyl, alkylidene, and imido functionalities.

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In metalloporphyrin chemistry, cis versus trans coordination geometries are generally assumed to be controlled by the nature of the metal ion, with the trans (or axial) arrangement being

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