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.

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Hydrazine dihydrochloride reacts with 3 equiv of Ph2PCl in tetrahydrofuran in the presence of triethylamine to give tris(diphenylphosphino)hydrazine (1) in 70% yield. Each nitrogen atom in 1 has a trigonal-planar environment according to X-ray analysis. Thermolysis of 1 at 130 degrees C results in the formation of two products: bis(diphenylphosphino)amine and octaphenylcyclotetraphosphazene. The interaction of free ligand 1 with NiBr2 affords a simple adduct [(Ph2P)2N-NH-PPh2]NiBr2, while its anionic (hydrazide) form undergoes rearrangement in a coordination sphere of divalent cobalt and nickel involving migratory insertion of the Ph2P group into a nitrogen-nitrogen bond. The reaction of 1 with cobalt bis(trimethylsilyl)amide, [(Me3Si)2N]2Co, yields the complex of phosphazenide-type (Me3Si)2N-Co[(Ph2PN)2PPh2] (2) in 86% yield. A similar reaction of 1 with nikelocene proceeds with substitution of one Cp ring to form durable 18-electron complex CpNi[(Ph2PN)2PPh2] (3).

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A number of novel phosphinohydrazines, iPr(2)P-NPh-NPh-H (1), iPr(2)P-NH-NH-PiPr(2) (2), iPr(2)P-NMe-NH-PiPr(2) (3), and H-NMe-NH-PiPr(2) (4), were prepared and characterized. The interaction of 1 with 1 equiv of n-BuLi afforded a complex compound [Li(DME)(3)][Li{(NPh-NPh-PiPr(2))-kappaN}(2)] (5). The reaction of 5 with NiBr(2) resulted in the formation of the first stable transition metal phosphinohydrazide [Ni{(NPh-NPh-PiPr(2))-kappa(2)N,P}(2)] (6). Similarly, the cobalt(II) derivative [Co{(NPh-NPh-PiPr(2))-kappa(2)N,P}(2)] (7) was prepared by the reaction of 1 with Co[N(SiMe(3))(2)](2). An X-ray study reveals formation of the complexes containing elongated N-N bonds (1.443(1), 1.466(2), and 1.470(2) A for 5, 6, and 7, respectively) as compared with the starting material 1 (1.407(1) A). Nickel phosphinohydrazide 6 has a square-planar cis configuration; the cobalt complex 7 possesses a square-planar centrosymmetric trans configuration. The half-sandwich nickel(II) complex [CpNi{(NPh-NPh-PiPr(2))-kappa(2)N,P}] (8) was prepared by prolonged heating of phosphinohydrazine 1 with NiCp(2) in toluene. The lithiation of 3 with n-BuLi resulted in the formation of an iminophosphoranate [LiN=PiPr(2)-NMe-PiPr(2)] (13) (in situ), which is the product of insertion of a PiPr(2) group into the nitrogen-nitrogen bond. The hydrolysis of 13 followed by the addition of CoCl(2) gave the phosphino-iminophosphoranato complex [CoCl(2){(HN=PiPr(2)-NMe-PiPr(2))-kappa(2)N,P}] (15) according to X-ray investigation. The phosphinohydrazine 3 reacted with FeX(2) in toluene to form adducts (1:1) [FeX(2){(PiPr(2)-NMe-NH-PiPr(2))-kappa(2)P,P'}] (X = Cl (9), Br (10)), while CoCl(2) gave the complex salt [{Co(PiPr(2)-NMe-NH-PiPr(2))-kappa(2)P,P'}(2)(mu-Cl)(3)][CoCl(3)(THF)] (11). A THF solution of complex 11 shows thermochromic behavior.

The reaction of 8-quinolylhydrazine with 2 equiv of Ph(2)PCl in the presence of Et(3)N gives 8-[(Ph(2)P)(2)NNH]-Quin (1) (Quin = quinolyl) in 84% yield. The heating of 1 at 130 °C for 1 h in toluene results in migration of the [Ph(2)PNPPh(2)] group to a carbon atom of the quinolyl fragment to form an isomer, 7-(Ph(2)P-N═PPh(2))-8-NH(2)-Quin (2). The same migration is caused by the addition of LiN(SiMe(3))(2) to 1. On the contrary, lithiation of 1 with n-BuLi followed by the addition of ZnI(2) (1:1) affords the aminoquinolyl-phosphazenide dinuclear complex [ZnI(8-Quin-NPPh(2)═N-PPh(2))-κ(3)N,N,P](2) (4), which is a result of P→N migration. Compound 1 itself reacts with ZnI(2) in THF to form 4 and protonated molecule 1·HI, which rearranges to the more stable iminobiphosphine salt (Ph(2)P-PPh(2)═N-NH-Quin-8)·HI. Zinc iodide reacts with 2 equiv of the lithium salt of 1 without rearrangement, to form homoleptic aminoquinolyl zinc complex Zn[{(Ph(2)P)(2)NN-Quin-8}-κ(2)N,N](2) (6). Solutions of 4 and 2 in dichloromethane show luminescence at 510 and 460 nm (quantum yields are 45% and 7%, respectively). DFT calculations were provided for possible isomers and their complexes.

Reactions of diphosphinohydrazines R-NH-N(PPh(2))(2) (R = tBu (1), Ph(2)P (3)) with some metalation reagents (Co[N(SiMe(3))(2)](2), LiN(SiMe(3))(2), La[N(SiMe(3))(2)](3), nBuLi, MeLi) were performed. Compound 1 was synthesized by the reaction of Ph(2)PCl with tert-butylhydrazine hydrochloride in 83% yield. This compound reveals temperature-dependent (31)P NMR spectra due to hindered rotation about the P-N bonds. Complicated redox reaction of 1 with Co[N(SiMe(3))(2)](2) proceeds with cleavage of the P-N and N-N bonds to form a binuclear cobalt complex [Co{HN(PPh(2))(2)-κ(2)P,P'}(2)(μ-PPh(2))](2) (2) demonstrating a short Co···Co distance of 2.3857(5) Å, which implies a formal double bond between the Co atoms. Strong nucleophiles (nBuLi, MeLi) cause fragmentation of the molecules 1 and 3, while reactions of 3 with lithium and lanthanum silylamides give products of the NNP → NPN rearrangement [Li{Ph(2)P(NPPh(2))(2)-κ(2)N,N'}(THF)(2)] (4) and [La{Ph(2)P(NPPh(2))(2)-κ(2)N,N'}{N(SiMe(3))(2)}(2)] (5), respectively. These complexes represent the first examples of a κ(2)N,N' bonding mode for the triphosphazenide ligand [(Ph(2)PN)(2)PPh(2)](-). DFT calculations showed large energy gain (52.1 kcal/mol) of the [NNP](-) to [NPN](-) anion rearrangement.

The lithium salt of 3,5‐dimethyl‐1‐phenyl‐1H‐pyrazole (PyrC6H4Li) reacts with (Et2N)2PCl to give the precursor [PyrC6H4P(NEt2)2] (2), which, after reaction with PCl3, affords PyrC6H4PCl2 (3) in 79 % yield. The phosphorus atom in 3 has four‐coordinate disphenoidal geometry with an axial arrangement of Cl atoms. The length of the hypervalent N–P bond in this compound [1.775(1) Å] is comparable to that of common single bonds. The structure of 3 is better described by canonical formulae containing charges on the N, P, and Cl atoms. The 1H NMR spectrum of 3 in CDCl3 shows five pairs of nonequivalent Me groups, which correspond to the positional isomers that exist in the equilibrium mixture. Compound 3 easily exchanges chlorine with methyl iodide to form the diiodo derivative 4 (PyrC6H4PI2) with nonequivalent P–I bonds. The reduction of 3 with aluminium foil or [GeCl2(diox)] gave cationic diphosphines [(PyrC6H4P)2(μ‐Cl)][AlCl4] (8) and [(PyrC6H4P)2(μ‐Cl)][GeCl3] (9), respectively, with a chloride bridge between the phosphorus atoms. Compounds 4, 8 and 9 show a disphenoidal arrangement around the hypervalent phosphorus atoms. The dichloro and diiodo derivatives 3 and 4 are destroyed on heating in pyridine to give diphosphines [(PyrC6H4PCl)2] (10) and [(PyrC6H4P)2(μ‐I)]+[I] (12), respectively, containing hypervalent (trivalent four‐coordinate) phosphorus. The crystal structure of 10 shows multiple C···C, C···Cl, H···H, and C···H short contacts between the adjacent molecules. Compound 3 exchanges chlorine for oxygen atoms on heating in dimethylformamide to give the dioxide PyrC6H4PO2 (13) with an N–PV distance [1.808(1) Å] even longer than that in 3.