Dinuclear palladium(II) and platinum(II) complexes of a readily accessible bicyclic diphosphane

The one-step synthesis (33 % isolated yield) of a novel bicyclic diphosphane, [P(CH₂)₂NC₆H₄(4-NMe₂)]₂, P−P(NMe₂), from the reaction of [P(CH₂OH)₄]Cl and H₂NC₆H₄(4-NMe₂) in methanol is described. Surprisingly, P−P(NMe₂) displays excellent air/solution stability (towards H₂O, CH₃OH) and can also function efficiently as a bridging ligand. Hence reaction of P−P(NMe₂) with [Pd(μ−Cl)(η³-allyl)]₂ (η³-allyl=C₃H₅, C₄H₇) or [Pd(μ−Cl)(κ²−C9H12N)]₂ affords the singly-bridged complexes {Pd(Cl)(η³-allyl)}₂ {μ-P−P(NMe₂)} 1 a/1 b and {Pd(Cl)(κ²−C₉H₁₂N)}2{μ-P−P(NMe₂)} 1 c whereas treatment with [MX₂(η⁴-cod)] (M=Pd, Pt; X=Cl, Br, I, Me; η⁴-cod=cycloocta-1,5-diene) gave (MX₂)₂{μ-P−P(NMe₂)}₂ 2 a–e in high yields. Protonation of 2 a–d with HBF₄ ⋅ OEt₂ gave the corresponding dimethylammonium salts 3 a–d. Single crystal X-ray studies have been undertaken on P−P(NMe₂), 1 b, 2 a, 2 b ⋅ 2CDCl₃, 2 d, 2 e, 3 a ⋅ 12CD₃CN and 3 b ⋅ 12CD₃CN. The P−P bond lengths in free/coordinated P−P(NMe₂) remain similar across all compounds studied here and no M ⋅⋅⋅ M contacts were observed within the planar M₂P₄ ring. In 3 a/3 b the BF₄− anion displays a unique secondary interaction with the inorganic six-membered M₂P₄ core.