Chemistry of Diazaphospholephosphines. 2. Exocyclic Phosphine−Sulfido, −Selenido, and −Imido Derivatives of a Diazaphospholephosphine System. Crystal and Molecular Structures of Two Diazaphospholephosphine Imines: 4-(Difluoro((p-cyanotetrafluorophenyl)imino)phosphorano)-2,5-dimethyl-2H-1,2,3σ2-diazaphosphole and 4-(Bis(dimethylamino)(((pentamethylcyclopentadienyl)dichlorotitanio)imino)phosphorano)-2,5-dimethyl-2H-1,2,3σ2-diazaphosphole

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Abstract
The substituted-exo-phosphine (X = F, NMe2, OCH2CF3) diazaphospholephosphines are exclusively oxidized at this center with either chalcogens (S, Se) or azides to phosphoranodiazaphospholes. Oxidation imparts a dramatic upfield shift of the phosphorus NMR signals and an increase in the 1JPC coupling constants within the ring. (Difluorophosphino)diazaphosphole was also oxidized with selected amines using diethyl azodicarboxylate (DAD) as the coupling agent. Bulky amines (e.g., 2,4,6-tri-tert-butylaniline (mes*)) gave the monomeric iminophosphorane whereas less bulky amines (p-toluidine) formed mostly the cyclic diazadiphosphetidine. The crystal and molecular structure of 4-(difluoro((p-cyanotetrafluorophenyl)imino)phosphorano)-2,5-dimethyl-2H-1,2,3σ2-diazaphosphole was determined: triclinic, P1̄ (No. 2), a = 7.2744(15) Å, b = 10.087(4) Å, c = 10.566(2) Å, α = 66.62(2)°, β = 77.60(2)°, γ = 78.14(3)°, V = 688.8(4) Å3, Z = 2. Final indices are R1 = 0.0368 and wR2 = 0.0968, and for all data, R1 = 0.0478, wR2 = 0.1033, and GOF = 1.067. The structure revealed two planar ring systems consisting of the diazaphosphole and the p-tetrafluorophenyl (tfbn) ring with an angle of 26.3° between the rings. The angle about the phosphine imine nitrogen (i.e., PN−tfbn) is relatively open (141.2(2)°), and the PN bond length is relatively short (1.514(2) Å). (((Trimethylsilyl)imino)(bis(dimethylamino))phosphorano)diazaphosphole gave, with Cp*TiCl3, [(η5-C5Me5)TiCl2(NP(NMe2)2(2,5-dimethyl-2H-1,2,3σ2-diazaphosphol-4-yl))], which was also characterized structurally: monoclinic, P21 (No. 4), a = 11.9477(11) Å, b = 8.4757(6) Å, c = 12.7567(11) Å, β = 108.824(8)°, V = 1222.7(2) Å3, Z = 2. Final indices are R1 = 0.0630 and wR2 = 0.1593, and for all data, R1 = 0.0768, wR2 = 0.1973, and GOF = 1.081. The Ti−N−P angle of 161.0(5)° was large, and the PN distance (1.592(6) Å) and the Ti−N distance (1.781(6) Å) were both slightly shorter than those in similar titanium complexes. The P−N single bond distances between the exo-phosphorus atom and the attached dimethylamino groups were also short (1.649 Å (average)). These short values suggest delocalized bonding character throughout the metal−ligand framework, possibly a consequence of additional conjugation through the diazaphosphole ring.

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