Organo-aluminum, zinc and magnesium derivatives of the imidotris(amido)phosphate Me3SiNP(NHtBu)3

Polyanionic Imido-P(V) Ligands: From Transition Metal Complexes to Coordination Driven Self-Assemblies

The chemistry of the imido-anions of the main group elements has been studied for more than three decades. The imido (NR)^- group is isoelectronic to the oxo (=O) group and can coordinate with metal ions through its lone pairs of electrons. The polyimido-P(V) anions are well explored as they resemble the phosphorus oxo moieties such as H₃ PO₄ , H₂ PO₄ ^- , HPO₄ ^2- and PO₄ ^3- species. These imido anions are typically generated using strong main group organometallic reagents such as ⁿ BuLi, Et₂ Zn, Me₃ Al and ⁿ Bu₂ Mg, etc. As a result, their coordination chemistry has been restricted to reactions in anhydrous aprotic solvents for a few main group metal ions. This account presents our findings on using certain soft transition metal such Ag(I) and Pd (II) for isolating these imido-P(V) anions as their corresponding self-assembled clusters and cages. Using the various salts of Ag(I) ions in reaction with 2-pyridyl (² Py) functionalized phosphonium salts and phosphoric triamides, we obtained the mono- and dianionic form of these imido ligands {[P(N² Py)₂ (NH² Py)₂ ]^- , [P(N² Py)₂ (NH² Py)]^- , [PO(N² Py)(NH² Py)₂ ]^2- } and derived interesting examples of tri, penta, hepta and octanuclear Ag(I) clusters. Interestingly, by using the salts of Pd (II) ions, the elusive imido-phosphate trianions of the type [(RN)₃ PO]^3- (R=^t Bu, ^c Hex, ⁱ Pr) were generated in a facile one pot reaction as their corresponding tri- and hexanuclear clusters of the type {Pd₃ [(NR)₃ PO](OAc)₃ }_n (n=1 or 2). These trianions acts as a cis-coordinated hexadentate ligand for a trinuclear Pd (II) cluster and serve as the polyhedral building units for constructing hitherto unknown family of neutral cages in tetrahedral {Pd₃ [(Nⁱ Pr)₃ PO]₄ (L)₆ } and cubic {Pd₃ [(Nⁱ Pr)₃ PO]₈ (L)₁₂ } structures in the presence of suitable linker ligands (L^2- ). These cages show interesting host-guest chemistry and post-assembly reactions. Remarkably, by employing chiral tris(imido)phosphate trianions, enantiopure chiral cages of the type [(Pd₃ X*)₄ (L)₆ ], ([X*]^3- =RRR- or SSS-[PO(N(*CH(CH₃ )Ph)₃ ]^3- ), were synthesized and used for the chiral-recognition and enantio-separation of small racemic guest molecules. Some of these chiral cages were also shown to exhibit polyradical framework structures. In future, these and other similar types of cages are envisioned as potential molecular vessels for performing the reactions in their confined environment. The enantiomeric cages can be probed for asymmetric catalysis and the separation of a range of small chiral molecules.

Reactivity of bis(organoamino)phosphanes with magnesium(ii) compounds

The reactivity of bis(organoamino)phosphanes with magnesium(ii) reagents is reported. The outcome of the reactions is influenced by a tautomeric H-shift in ligand backbones.

Facile formation of stable tris(imido)phosphate trianions as their tri- and hexanuclear Pd(II) complexes in protic solvents

Employing Pd(OAc)2, a facile deprotonation route to access the highly basic tris(alkylimido)phosphate trianions, [(RN)3PO](3-) (R = (t)Bu, (c)Hex, or (i)Pr), analogous to the orthophosphate (PO4(3-)) ion in polar and in protic solvents has been achieved. Trinuclear and prismatic Pd(II) clusters of these imido trianions having the formula {Pd3[(NR)3PO](OAc)3}n (n = 1 or 2) or as mixed-bridged clusters of the type {Pd3[(N(i)Pr)3PO](OAc)2(OR')}2 (R' = Me or H) were isolated exclusively in all these reactions in which the trianionic species acts as a tripodal chelating ligand to the trinuclear Pd3 unit. Reactivity studies aiming at the Pd(II) atoms in these clusters with nucleophilic reagents, such as primary amines (R″NH2), have led to a new trimeric cluster with the formula {Pd3[(NR)3PO](OAc)3(R″NH2)3} in which the tripodal coordination of the Pd-Nimido moieties remained unaffected, exemplifying the robustness of the Pd3 unit in all these clusters. We have also shown the catalytic activity of these Pd(II) complexes in Mizoroki-Heck type coupling reactions in the presence of Cu(OAc)2.