Abstract
Our group have reported the synthesis of low-coordinate and low-valent quintuply-bonded dichromium complex Cr2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (1). Treatment of 1 with alkynes afforded a family of alkyne-complexed compounds (μ-κ2-(CH3)3SiCCH)Cr2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (2), (μ-κ2-(CH3)3CCCH)Cr2[μ- κ2-HC(N-2,6-iPr2C6H3)2]2 (3) and (μ-κ2-(C6H5)CCH)Cr2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (4), which all feature a Cr-Cr quadruple bond. When treatment of 1 with three equivalents of ethynyltrimethylsilane, we obtain an inverted-sandwich compound [μ-η6:η6-(1,3,5-(SiMe3)3C6H3)]Cr2[κ2-HC(N-2,6-iPr2C6H3)2]2 (5). This result is only observed in the reaction with 1 and ethynyltrimethylsilane. Surprisingly, after 5 dissolved in tetrahydrofuran or reacts with 2,4,6-trimethylbenzonitrile, 5 turns back to 1. Treatment of 1 or 5 with a series of benzonitrile, they show identical reacitivity and afforded compounds with same structure (μ-κ1C:κ2N-PhCN)2(κ1-PhCN)2Cr2[μ-κ2-HC( -N-2,6-iPr2C6H3)2]2 (6), (μ-κ1C:κ2N-o-tolylCN)2(κ1-o-tolylCN)2Cr2[μ-κ2-HC(N-2,6-iP -r2C6H3)2]2 (7), (μ-κ1C:κ2N-p-tolyl-CN)2(κ1-p-tolylCN)2Cr2[μ-κ2-HC(N-2,6-iPr2C6H3 -)2]2 (8) and (μ-κ1C:κ2N-2-methoxy-m-tolylCN)2(κ1-2-methoxy-m-tolylCN)2Cr2[μ-κ2- -HC(N-2,6-iPr2C6H3)2]2 (9). 5 show excellent yield and regioselectivity in the cyclotrimerization with alkynes. Last, treatment of 1 with pyridine-borane generated Cr2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2(μ-H)(μ-κ2-C5H4BH3) (10) during C-H bond activation. (μ-η6:η6-C7H8)[Cr(Nacnac)]2 (11) (Nacnac = HC((CMe)NC6H3-iPr2)2), an inverted-sandwich dichromium compelex is prepared. Treatment 11 with 2-methylbenzonitrile and 2,4,6-trimethylbenzonitrile afforded Cr(Nacnac)(o-tolylCN) -[NH(3-(o-tolyl)isoquinoline)] (12) and Cr(Nacnac)[κ2-HN(C-2,4,6-Me3C6H2)2NH] (13). Both reactions involve C-C coupling. Treatment mononuclear chromium complex Cr[κ2-HC(N-2,6-iPr2C6H3)2]2 (14) with CoCl¬2 obtained hetero-dinuclear complex Co[κ1-HC(N-2,6-iPr2C6H3)2][μ-κ2-HC( -N-2,6-iPr2C6H3)2]Cr[κ2-HC(N-2,6-iPr2C6H3)2] (15).