Water-Soluble Organometallic Compounds. 6.¹Synthesis, Spectral Properties, and Crystal Structures of Complexes of 1,3,5-Triaza-7-phosphaadamantane with Group 10 Metals

Abstract

The syntheses of a variety of group 10 metal complexes of the water-soluble phosphine triazaphosphaadamantane (PTA) are described. Treatment of Ni(NO 3 ) 2 with NaNO 2 and PTA provides the nitrosyl complex [Ni(NO)(PTA) 3 ]NO 3 ( 1 ). Complex 1 is soluble in water, DMSO, and CH 3 CN but insoluble in THF, acetone, or hydrocarbons. X-ray crystallography shows the nitrosyl ligand to be coordinated in a near linear mode (∠Ni−N−O = 171.5(4)°) with a Ni−N bond length of 1.653(4) Å. Concordantly, the υ(NO) vibration in H 2 O occurs at 1830 cm - 1 . The series of zerovalent M(PTA) 4 (M = Ni, Pd, Pt) complexes, 2, 3, and 6 have been prepared in good yields by several procedures: (i) the ligand exchange reaction of Ni(cod) 2 with PTA; (ii) the reduction of PdCl 2 or PtCl 2 with hydrazine in the presence of PTA; and (iii) the ligand exchange reaction of Pt(PPh 3 ) 4 with PTA. All three derivatives are very water soluble (0.30 M) and resistant to PTA dissociation in solution at ambient temperature. Complexes 2, 3, and 6 can be crystallized from 0.10 M HCl to afford the nitrogen-protonated derivatives, [M(PTAH) 4 ]Cl 4 . These salts were characterized by X-ray crystallography and shown to exist as slightly distorted tetrahedra with one nitrogen atom of each PTA ligand protonated. The M−P bond lengths are shorter than those found in related derivatives containing poorer electron-donating and/or sterically more encumbering phosphine ligands. The cis -MCl 2 (PTA) 2 (M = Pd and Pt) derivatives, 4 and 7, were obtained by the metathesis reaction of (NH 4 ) 2 PdCl 4 or K 2 PtCl 4 with PTA in refluxing ethanol. When the palladium reaction was carried out in a large excess of PTA, formation of the zerovalent Pd(PTA) 4 complex occurred via the intermediacy of the [Pd(PTA) 3 Cl] + cation as indicated by 31 P NMR and mass spectrometry. The X-ray structures of the Pd(II) and Pt(II) derivatives, cis -PdCl 2 (PTA) 2 and [ cis -PtCl 2 (PTAH) 2 ]Cl 2, revealed these to exist as slightly distorted square planar complexes where the P−M−P angles are expanded to 94.4°. The platinum derivative, which contains the nitrogen protonated PTA ligands, displays an extensive array of hydrogen bonding and electrostatic interactions involving water, PTA, and HCl.