Water-soluble organometallic compounds .6. Synthesis, spectral properties, and crystal structures of complexes of 1,3,5-triaza-7-phosphaadamantane with group 10 metals
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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 3CN but insoluble in THF, acetone, or hydrocarbons. X-ray crystallography shows the nitrosyl ligand to be coordinated in a near linear mode (ZNi-N-O = 171.5(4)) with a Ni-N bond length of 1.653(4) . Concordantly, the v(NO) vibration in H 2O 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) 2PdCl 4 or K 2PtCl 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) 3Cl] + cation as indicated by 31P 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.