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

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Abstract

The syntheses of a variety of group 10 metal complexes of the water-soluble phosphine triazaphosphaadamantane (PTA) are described. Treatment of Ni(NO3)2 with NaNO2 and PTA provides the nitrosyl complex [Ni(NO)(PTA)3]NO3 (1). Complex 1 is soluble in water, DMSO, and CH3CN 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 H2O 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 PdCl2 or PtCl2 with hydrazine in the presence of PTA; and (iii) the ligand exchange reaction of Pt(PPh3)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]Cl4. 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-MCl2(PTA)2 (M = Pd and Pt) derivatives, 4 and 7, were obtained by the metathesis reaction of (NH4)2PdCl4 or K2PtCl4 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-PdCl2(PTA)2 and [cis-PtCl2(PTAH)2]Cl2, 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.

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