Phosphine-Based Platinum(II) Hydroxo and Oxo Complexes¹

Abstract

The platinum(II) hydroxo complexes, [L2Pt(μ-OH)]2(BF4)2 (1), have been prepared from the reaction of L2PtCl2 with AgBF4 for L2 = dppm, dppp, dppb, 2PMe2Ph, and Bu t 2bpy (dppm = bis(diphenylphosphino)methane, dppe = bis(diphenylphosphino)ethane, dppp = bis(diphenylphosphino)propane, dppb = bis(diphenylphosphino)butane, Bu t 2bpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine). The trifluoroacetate (L2 = dppp) and the nitrate (L2 = Bu t 2bpy) salts were also prepared. Two of these new hydroxo complexes, as well as the previously known PPh3 complex, were structurally characterized. Crystals of [(PPh3)2Pt(μ-OH)]2(BF4)2 from CH2Cl2/ether are monoclinic (C2/m) with a = 17.183(5) Å, b = 18.243(4) Å, c = 13.539(4) Å, β = 130.66(2)°, and Z = 2. Crystals of [(dppm)Pt(μ-OH)]2(BF4)2·2DMF from DMF/Et2O are monoclinic (P21/n) with a = 17.193(6) Å, b = 9.341(5) Å, c = 18.666(7) Å, β = 98.73(2)°, and Z = 2. Crystals of [(dppb)Pt(μ-OH)]2(BF4)2·4MeOH from MeOH/Et2O are triclinic (P1̄) with a = 12.547(13) Å, b = 12.858(14) Å, c = 13.039(20) Å, α = 62.89(11)°, β = 63.05(11)°, γ = 60.87(12)°, and Z = 1. The structures of the binuclear dications are all similar, having planar P2Pt(μ-OH)2PtP2 cores with pseudo-D 2 h symmetry. For all but the dppm complex, addition of 2 equiv of LiN(SiMe3)2 results in deprotonation of the hydroxo groups and formation of the oxo complexes [L2Pt(μ-O)]2. The isolated oxo complexes are associated with one (L = PPh3) or two (L = PMe2Ph; L2 = dppe, dppp, dppb, Bu t 2bpy) LiX units (X = BF4 or CF3CO2) by interaction of the oxo ligands with the Li cations. The structure of [(PPh3)2Pt(μ-O)]2·LiBF4 (2) was determined. Crystals of 2·0.5C7H8 from toluene are monoclinic (C2/c), with (173 K) a = 20.469(8) Å, b = 18.085(9) Å, c = 18.152(8) Å, β = 90.34(6)°, and Z = 4. The structure consists of two edge-shared square planar Pt atoms folded at the edge with cis-phosphines and bridging oxygen atoms. The bridging oxo oxygen atoms are coordinated to the Li cation of a LiBF4 contact ion pair. Two fluorine atoms of the BF4 ion also coordinate to the Li cation, resulting in a flattened tetrahedral environment about the Li cation. The oxo complex [(PMe2Ph)2Pt(μ-O)]2·(LiBF4)2 is unstable in solution and converts to the μ3-oxo complex [(L2Pt)3(μ3-O)2](BF4)2 (5) (L = PMe2Ph). Crystals of 5 from THF are orthorhombic (Pbna), with (173 K) a = 16.792(4) Å, b = 17.710(5) Å, c = 19.648(6) Å, and Z = 4. The core structure of the dication consists of a dioxo-bicapped Pt3 triangle. Deprotonation of the dppm hydroxo complex 1 (L2 = dppm) occurs at the dppm methylene group and not at the hydroxo group. The resulting neutral hydroxo complex [(dppm-H)Pt(μ-OH)]2 (6) (dppm-H = bis(diphenylphosphino)methanide) is further deprotonated in THF at the OH group, giving the structurally characterized anionic oxo complex [(dppm-H)Pt(μ-O)]2[Li(THF)2]2 (7). Crystals of 7·4THF from THF are monoclinic (P21/c), with (173 K) a = 10.534(2) Å, b = 21.016(2) Å, c = 18.402(4) Å, β = 103.41(1)°, and Z = 2. The structure has a planar core with the deprotonation of t...

Hydroxo and Oxo Complexes of Platinum(II) Stabilized by Phosphanes: Synthesis and Characterization − X‐ray Structures of cis‐[L2Pt(μ‐OH)]2(NO3)2 (L = PMe2Ph, PMePh2) and [{cis‐(PMe2Ph)2Pt}3(μ‐O)2]Cl2

“…A large excess of Cl Ϫ ions leads to the formation of cis-[L 2 PtCl 2 ] as the main product, whereas relatively good yields of the oxo complex are formed when the molar ratio n (Cl Ϫ ) /n (hydroxo complex) approaches the value of 2:1. This finding contrasts the observations reported by Bushnell for the strictly related hydroxo complex stabilized by PEt 3 . [4] In that case, addition of LiCl to a solution of [cis-(PEt 3 ) 2 Pt(µ-OH)] 2 2ϩ , in a 2:1 molar ratio, gave the substitution product cis-[(PEt 3 ) 2 PtCl 2 ] and about half of the starting hydroxo complex remained unreacted.…”

“…This trend probably reflects the different repulsion effects at the metal centers due to the diverse basicity of the PR 3 ligands. [3] As found in the PMe 3 analogue, in 1a the hydroxo ligands interact via hydrogen-bonding with the nitrate anions. In particular, the atoms that are involved in this hydrogenbonding interaction are O(6) (at x, y, 1 Ϫ z) in unit I (O···O separation of 2.74 Å and an OϪH···O angle of 167°) and O(2) (at x, y ϩ 1, z) in unit II (separation of 2.79 Å and an angle of 178°).…”

“…The O···O distance is relatively short in the PMe 3 derivative (2.54 Å ), however, this distance is longer in 1a and 2, 2.61 Å and 2.64 Å , respectively; the latter value is the same as that observed for the structurally analogous complex that is stabilized by NH 3 ligands, [7] and only slightly shorter than that found in the PPh 3 derivative (2.66 Å ). [3] An increase in the O···O separation is accompanied by a decrease in the Pt···Pt distance; 3.222 Å (average) in 1a, 3.174(1) Å in 2 and 3.261 Å in the PMe 3 complex. This trend probably reflects the different repulsion effects at the metal centers due to the diverse basicity of the PR 3 ligands.…”

“…An exception is represented by the adduct [cis-L 2 Pt(µ-O)] 2 ·2LiBF 4 (L ϭ PMe 2 Ph), which decomposes in THF to give [{cis-L 2 Pt} 3 (µ-O) 2 ](BF 4 ) 2 (Scheme 1), the trinuclear species in which each oxygen atom is symmetrically coordinated to three [L 2 Pt] 2ϩ units. [3] X-ray diffraction methods. Under the same experimental conditions, the structurally analogous hydroxo complex, stabilized by the less basic and more hindered PMePh 2 2 ] 2ϩ species in which the relative quantity of the two compounds is strongly dependent on the amount of added chloride.…”

Coordination Modes of 9‐Methyladenine in cis‐Platinum(II) Complexes with Dimethyl(phenyl)phosphanes as Ancillary Ligands − Synthesis and Characterization of cis‐[PtL2(9‐MeAd)2](NO3)2, cis‐[PtL2{9‐MeAd(−H)}]3(NO3)3, and cis‐[L2Pt{9‐MeAd(−H)}PtL2](NO3)3

“…As would be expected, [8] solutions of 1 in water are acidic as a result of an acid/base equilibrium [Equation (2)] and the dinuclear hydroxo complex 6 is obtained in good yield when the solutions are neutralized with a strong base. [8,9] 2 cis-[PtL 2 …”