Water-Soluble Organometallic Compounds. 6. Synthesis, Spectral Properties, and Crystal Structures of Complexes of 1,3,5-Triaza-7-phosphaadamantane with Group 10 Metals

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.