Functionalization Reactions Characteristic of a Robust Bicyclic Diphosphane Framework

The 3,4,8,9-tetramethyl-1,6-diphospha-bicyclo-[4.4.0]­deca-3,8-diene
(P2(C6H10)2) framework
containing a P–P bond has allowed for an unprecedented selectivity
toward functionalization of a single phosphorus lone pair with reference
to acyclic diphosphane molecules. Functionalization at the second
phosphorus atom was found to proceed at a significantly slower rate,
thus opening the pathway for obtaining mixed functional groups for
a pair of P–P bonded λ5-phosphorus atoms.
Reactivity with the chalcogen-atom donors MesCNO (Mes = 2,4,6-C6H2Me3) and SSbPh3 has allowed
for the selective synthesis of the diphosphane chalcogenides OP2(C6H10)2 (87%), O2P2(C6H10)2 (94%), SP2(C6H10)2 (56%), and S2P2(C6H10)2 (87%).
Computational studies indicate that the oxygen-atom transfer reactions
involve penta-coordinated phosphorus intermediates that have four-membered
{PONC} cycles. The P–E bond dissociation enthalpies in EP2(C6H10)2 were measured via
calorimetric studies to be 134.7 ± 2.1 kcal/mol for P–O,
and 93 ± 3 kcal/mol for P–S, respectively, in good agreement
with the computed values. Additional reactivity with breaking of the
P–P bond and formation of diphosphinate O3P2(C6H10)2 was only observed
to occur upon heating of dimethylsulfoxide solutions of the precursor.
Reactivity of diphosphane P2(C6H10)2 with azides allowed the isolation of monoiminophosphoranes
(RN)­P2(C6H10)2(R = Mes,
CPh3, SiMe3), and treatment with additional
MesN3 yielded symmetric and unsymmetric diiminodiphosphoranes
(RN)­(MesN)­P2(C6H10)2 (91%
for R = Mes). Metalation reactions with the bulky diiminodiphosphorane
ligand (MesN)2P2(C6H10)2 (nppn) allowed for the isolation and characterization
of (nppn)­Mo­(η3-C3H5)­Cl­(CO)2 (91%), (nppn)­NiCl2 (76%), and [(nppn)­Ni­(η3-2-C3H4Me)]­[OTf] showing that these
ligands provide an attractive preorganized binding pocket for both
late and early transition metals.

含有P-P键的3,4,8,9-四甲基-1,6-二磷杂双环[4.4.0]癸-3,8-二烯（P2(C6H10)2）骨架，相较于无环二膦分子，在单磷孤对电子的官能化反应中展现出前所未有的选择性。研究发现，第二个磷原子的官能化反应速率显著更低，由此为合成P-P键连的λ5-磷原子对的混合官能化产物提供了可行途径。

与硫属原子给体MesCNO（Mes=2,4,6-C6H2Me3）及SSbPh3的反应，可选择性合成二膦硫属化物OP2(C6H10)2（产率87%）、O2P2(C6H10)2（产率94%）、SP2(C6H10)2（产率56%）及S2P2(C6H10)2（产率87%）。

计算化学研究表明，氧原子转移反应涉及带有四元{PONC}环的五配位磷中间体。通过量热实验测得EP2(C6H10)2中的P-E键解离焓：P-O键为134.7±2.1 kcal/mol，P-S键为93±3 kcal/mol，与理论计算值吻合良好。仅在将前驱体的二甲基亚砜溶液加热时，才会观察到P-P键断裂并生成二膦酸酯O3P2(C6H10)2的副反应。

二膦P2(C6H10)2与叠氮化物的反应可分离得到单亚胺基膦烷(RN)P2(C6H10)2（R=Mes、CPh3、SiMe3）；若继续加入过量MesN3，则可得到对称与不对称的二亚胺基二膦烷(RN)(MesN)P2(C6H10)2（当R=Mes时产率为91%）。以位阻型二亚胺基二膦烷配体(MesN)2P2(C6H10)2（缩写为nppn）进行金属化反应，可分离并表征得到(nppn)Mo(η³-C3H5)Cl(CO)2（产率91%）、(nppn)NiCl2（产率76%）及[(nppn)Ni(η³-2-C3H4Me)][OTf]，证明此类配体可为前过渡金属与后过渡金属均提供结构预组织的优良结合口袋。