[2+2+1] Cycloadditions of Bis(dialkylamino)acetylenes with SiI 2 (Idip): Syntheses and Reactivity Studies of Unprecedented 2,3,4,5‐Tetraamino‐1 H ‐siloles

A novel method for the synthesis of 1 H ‐siloles is presented. It involves a [2+2+1] cycloaddition of the ynediamines R 2 NCCNR 2 (R=Me, Et) with SiI 2 (Idip) (Idip=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) to afford the orange‐colored, highly water‐sensitive 1,1‐diiodo‐2,3,4,5‐tetraamino‐1 H ‐siloles SiI 2 {C 4 (NR 2 ) 4 } ( 1‐I : R=Me; 2‐I R=Et). Treatment of 2‐I with an excess of SiBr 4 afforded after I/Br exchange the 1,1‐dibromo‐1 H ‐silole SiBr 2 {C 4 (NEt 2 ) 4 } ( 2‐Br ). The 1 H ‐siloles 1‐I , 2‐I , and 2‐Br were fully characterized and their molecular structures determined by single‐crystal X‐ray diffraction. The compounds feature a slightly twisted five‐membered silacyclopenta‐2,4‐diene ring and a double/single CC bond alternation in the diene fragment. Reaction of 2‐I with the N‐heterocyclic carbene IMe 4 (IMe 4 =1,3,4,5‐tetramethylimidazolin‐2‐ylidene) leads, after displacement of the iodide groups, to the unprecedented diiodide salt [Si(IMe 4 ) 2 {C 4 (NEt 2 ) 4 }](I) 2 ( 3 ), containing a 1 H ‐silole dication with a four‐coordinate Si IV center. The crystal structure of 3 reveals similar bonding characteristics for the dicationic 1 H ‐silole to those of the neutral 1 H ‐siloles 1‐I–2‐Br . Two‐electron reduction of 3 with C 8 K affords, after elimination of one IMe 4 group, the thermolabile, carbene‐stabilized 1‐silacyclopentadien‐1‐ylidene Si{C 4 (NEt 2 ) 4 }(IMe 4 ) ( 4 ), which was characterized by elemental analysis and 1 H, 13 C{ 1 H}, and 29 Si{ 1 H} NMR spectroscopies.