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Treatment of Mes2BOH (1) with «-BuLi in hexane/ether affords a suspension of LiOBMes2, which can be crystallized from THF solution as the dimer [|Li(THF)OBMes2¡2] (2). Treatment of a slurry of anhydrous CoCl2 in THF with 2 equiv of 2 gives the complex [Co{OBMes2)2Li(THF)2Cl2Li(THF)2] (3) in good yield. The X-ray crystal structures of 1-3 are also reported. The structure of 1 is the first for a diorganoboronous acid, and it exists in the solid state as hydrogen-bonded tetramers. The lithium derivative 2 is the first structurally characterized example of a metal salt of a boronous acid, and it possesses a dimeric structure previously seen only with very bulky -OC(Z-Bu)3 and -OC6H2-2,6-i-Bu2-4-Me salts. The complex 3 has cobalt pseudotetrahedrally bound to two -OBMes2 and Cl" ligands, which also form bridges to two Li+ ions. Each Li+ is also pseudotetrahedrally coordinated, with two THF donors as the remaining ligands in each case. Crystallographic data with Mo Kce radiation ( = 0.71069 Á) at

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The synthesis and characterization of the aminoboranes HNRBMes2 (R = Ph, 1; R = Mes, 2), the lithium salts Li(Et2G)2NRBMes2 (R = Ph, 3; R = Mes, 4), and the transition-metal derivatives (THF)(Et20)2LiClCo[NPhBMes2}2 (5) and MnjNMesBMes2)2i3PhMe ( 6) are reported. The X-ray crystal structures of 1, 3, 5, and 6 are also described. The structures reveal that all the nitrogen and boron centers within the ligands are planar and that the twist angles between these planes are small. The multiple character of the B-N bond remains essentially unchanged in all compounds. As a result the boryl-substituted amide ligand is predicted to have poor -bridging characteristics. This is borne out by the structures of 3, 5, and 6 that are the first structurally characterized transition-metal complexes of a borylamide ligand. An interesting consequence of the low bridging tendency of the -NRBMes2 ligand is the isolation of the two-coordinate Mn(II) complex 6, whereas more conventional amide ligands such as -N(SiMe3)2 and -NPh2 have led to bridged products in the solid. Crystal data [Mo Ka

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