N,N′-Fused Bisphosphole: Heteroaromatic Molecule with Two-Coordinate and Formally Divalent Phosphorus. Synthesis, Electronic Structure, and Chemical Properties

The reduction of 6,12-dichloro-1,2,3,4,7,8,9,10-octahydro-6H,12H-[1,2,3]­benzodiazaphospholo­[2,1-a]­[1,2,3]­benzodiazaphosphole (3) by metallic magnesium in tetrahydrofuran (THF) affords the N,N′-fused bisphosphole 1 in 92% yield. The compound reveals a novel type of 10π-electron heteroaromatic system [NICS(0) = −11.4], containing a two-coordinate and formally divalent phosphorus atom. Compound 1 possesses a much higher coordination activity than many other diazaphospholes. This is caused by a novel type of complexation to a metal ion wherein the lone phosphorus pairs are not involved in metal coordination. Instead, the 10π-electron heteroaromatic system provides two electrons for P → M bond formation. Polarization of the ligand results in the formation of extended molecular associates or cluster compounds. Complexes of 1 with mercury dichloride [{(1)3HgCl}2(μ6-Cl)]+Cl– (7) and tin dichlorides [1·SnCl2(PhMe solvate)] (8a) and [1·SnCl2] (8b) are, in fact, supramolecular in nature, containing multiple intermolecular short contacts. Crystals of complex 8a containing short Sn···Sn packing interactions were converted reversibly to metallic tin after workup with THF. The simple mixing of 1 and 3 (1:1) gave a P–P bridging dimeric species prone to easy dissociation. The addition of GeCl2(diox) to the equimolar mixture of 1 and 3 shifted the equilibrium to the formation of a poorly soluble salt-like dimer 6, which is, in fact, a stacked 18π-electron dication having a through-space delocalization of π electrons.以金属镁在四氢呋喃（tetrahydrofuran, THF）中还原6,12-二氯-1,2,3,4,7,8,9,10-八氢-6H,12H-[1,2,3]苯并二氮杂磷杂环[2,1-a][1,2,3]苯并二氮杂磷杂环（3），以92%的收率得到N,N′-稠合双磷杂环1。该化合物展现出一类新型10π电子杂芳环体系[NICS(0) = −11.4]，其中包含一个两配位且形式氧化态为二价的磷原子。化合物1的配位活性远高于多数其他二氮杂磷杂环，这源于一种新型金属离子络合模式：磷原子的孤对电子并未参与金属配位，而是由该10π电子杂芳环体系提供两个电子以形成P→M键。配体的极化作用可形成延伸的分子聚集体或簇合物。1与二氯化汞[{(1)3HgCl}2(μ6-Cl)]+Cl–（7）、二氯化锡的配合物[1·SnCl2(甲苯溶剂化物)]（8a）以及[1·SnCl2]（8b），本质上均为超分子体系，包含多个分子间短程相互作用。含有短程Sn···Sn堆积相互作用的配合物8a晶体，经四氢呋喃后处理后可可逆转化为金属锡。将1与3按1:1的比例简单混合，可得到易解离的P-P桥联二聚体。向1与3的等摩尔混合物中加入二氯化锗(二氧六环络合物，GeCl2(diox))，平衡会向生成难溶性类盐二聚体6的方向移动；该二聚体本质上为堆叠型18π电子双阳离子，其π电子存在空间离域。