Alan Pidcock

Preparation of arylplatinum(II) complexes. The interaction of dichloro-(η-cyclo-octa-1,5-diene)platinum(II) and aryltrimethylstannanes

One or both chloride ligands of [Pt(cod)Cl2](cod = cyclo-octa-1,5-diene) can be readily and selectively replaced by aryl groups by treatment of the complex with aryltrimethylstannanes in dichloromethane or sym-tetrachioroethane. Use of 1 mol of SnMe3R usually gives the monoaryl complexes in high yield [e.g. R = 2-furyl, 2-thienyl, benzofuran-2-yl, 2-benzothienyl, 1,2-dihydrobenzocyclobuten-3-yl, or C6H4X (X = H, p-MeO, p-Cl, p-F, p-Me3Si, or p-Me)], but for R =η6-p-MeC6H4Cr(CO)3 the diaryl complex is formed. Use of 2 mol of SnMe3R gives the diaryl complexes in good yield [e.g. R as above; plus C6H4X (X =o-MeO, m-MeO, m-F3C, p-Br, m-F, m-Cl, and p-O2N)], but, for steric reasons, with R = C6H2Me3-2,4,6 only the monoaryl complex is formed. The reactivity of the SnMe3R compounds generally parallels the ease of electrophilic substitution at the corresponding R–H bonds. The arylation method has substantial advantages over those using aryl Grignard or lithium reagents. Aryl compounds, MMe3R, of other Group 4 metals undergo analogous reactions, the reactivity decreasing in the sequence (M =) Pb > Sn Ge > Si. While mixed diaryl complexes can sometimes be made in good yield {e.g.[Pt(cod)-(2-C4H3S)(2-C4H3O)] from [Pt(cod)(2-C4H3S)Cl] and SnMe,(2-C4H3O)}, such preparations can be complicated by exchange of aryl groups between platinum centres; e.g.(i) reaction of [Pt(cod)(2-C4H3S)2] with [Pt(cod)Cl2] followed by addition of 1,2-bis(diphenylphosphino)ethane (dppe) gives [Pt(2-C4H3S)Cl(dppe)] in ca. 100% yield, (ii)[Pt(cod)(2-C8H5O)2] and [Pt(cod)(C6H4Cl-m)2] similarly give some [Pt(2-C8H5O)(C6H4Cl-m)(dppe)], and (iii)[Pt(cod)(3-C8H7)Cl] and SnMe3(C6H4Me-p) similarly give some [Pt(3-C8H7)2(dppe)] and [Pt(C6H4Me-p)2-(dppe)](3-C8H7= 1,2-dihydrobenzocyclobuten-3-yl). The olefin ligand is readily displaced from the aryl com-plexes by neutral ligands, and a wide range of [PtR(Cl)L2] and [PtR2L2] complexes with L =½ dppe or PPh3 have been made. The i.r. and 1H, 13C-{1H}, and 31P-{1H} n.m.r. spectra of the products are discussed. For cis-[ Pt(C6H4X-p)2(PPh3)2] complexes the values of 1J(Pt–P) show a good correlation with σI constants. The norbornadiene (nbd) complex [Pt(nbd)Cl2] reacts with SnMe3(2-C4H3O) to give [Pt(2-C4H3O)(nbd)Cl] in 91% yield, but the corresponding palladium complex [Pd(nbd)Cl2] reacts with SnMe3R (R = C6H4OMe-p or C6H4Me-p) to give a dimeric chloride-bridged complex in which the aryl group is attached to the organic ligand.

The role of bivalent tin compounds in platinum co-ordination chemistry; X-ray structure of [Pt{Sn(NR′2)2}3], trans-[(Pt(µ-Cl)(PEt3){SnCl(NR′2)2})2], and (SnClR2)2[R = CH(SiMe3)2, R′= SiMe3]

Bivalent tin compounds SnX2 behave in one of three ways towards platinum substrates: (a) as neutral ligands, (b) as co-ordinatively unsaturated fragments by inserting into Pt–Cl bonds, and (c) as reducing agents; these features are illustrated, inter alia, by X-ray data on the three title compounds.

Platinum–phosphorus bond lengths and nuclear magnetic resonance coupling constants in complexes of tri(n-alkyl)- and tricyclohexylphosphines. Crystal and molecular structure of trans-di-iodobis(trimethylphosphine)platinum(II)

The crystal and molecular structure of trans-[Ptl2(PMe3)2] has been determined. Crystals are monoclinic, space group P21/n, with a= 8.845(6), b= 10.298(8), c= 7.936(5)A, β= 95.12(4)°, and Z= 2. Intensities have been measured by diffractometer and the structure solved by the heavy-atom method and refined to R 0.041. The crystal comprises discrete centrosymmetric molecules wrth only small deviations from square-planar co-ordination [Pt–P 2.315(4) and Pt–I 2.599(2)A]. The intramolecular H ⋯ I distances are longer than in trans-[PtI2{P(C6H11)3}2]. The configuration of the cyclohexyl groups of the P(C6H11)3 ligands is determined by H ⋯ H interactions and leads to strong H ⋯ I interactions between hydrogen atoms on two α-carbon atoms and the Iodide ligands, with consequent lengthening of the Pt–P and Pt–I bonds in trans-[PtI2{P(C6H11)3}2]. The coupling constants 1J(Pt–P) for trans-di-iodo(tricyclohexylphosphine) complexes are larger than expected, probably due to large |ΨPt,6s(0)|2/(3ΔE) terms for complexes with bonds lengthened by steric repulsions.

Use of aryltin compounds in the preparation of diaryl- and diaroyl-di-µ-chloro-bis(triorganophosphine)diplatinum(II) complexes

The complexes cis-[Pt(C2H4)Cl2L](L = triorganophosphine) react with compounds SnRMe, (R = aryl)(1 mol equivalent) to give the chloride-bridged arylplatinum complexes [Pt2R2Cl2L2], which exist in solution as mixtures of cis and trans isomers. The [Pt2R2Cl2L2] complexes react with ligand species L′[L′= NCMe, SBut2, pyridine, NBunH2, AsPh3, PEt3, PBun3, PPh3, or P(OPh)3] to give the mononuclear complexes [PtR(Cl)L(L′)], and this represents an excellent route to mononuclear complexes having four different ligands on platinum. Cyclo-octa 1,5-diene (cod), however, gives [PtR(Cl)L2] and [Pt(cod)R(Cl)], while 2,2′-bipyridyl (bipy) gives the salt [PtR(bipy)L]Cl. Sodium thiocyanate reacts with [Pt2(C6H4Me-p)2Cl2(PEt2Ph)2] to give the thiocyanate-bridged [Pt2(C6H4Me-p)2(PEt2Ph)2(µ-SCN)2], and [NEt4]Cl reacts with [Pt2(C6H4Bun-p)2(PMe2Ph)2] to give the salt [NEt4][Pt(C6H4Bun-p)Cl2(PMe2Ph)]. Excess of SnRMe3 causes decomposition of [Pt2R2Cl2L2] to give the mononuclear complexes [PtR(Cl)L2]. The carbonyl complexes cis-[Pt(CO)Cl2L] react with SnRMe3 to give the binuclear aroyl complexes [Pt2(COR)2Cl2L2], which also exist in solution as mixtures of cis and trans isomers. These complexes react with neutral ligand species L′= NBunH2 or P(OPh)3 to give the mononuclear complexes [Pt(COR)Cl(L)L′]. but cod reacts with [Pt2(COC6H4But-p)2Cl2(PMe2Ph)2] to give [Pt(COC6H6But-p)Cl-(PMe2Ph)2]. Again excess of SnRMe3 causes decomposition, to give [Pt(COR)Cl(L)] complexes. Heating of the aroyl complex [Pt2(COC6H4Me-p)2Cl2(PEt3)2] gives some of the corresponding aryl complex [Pt2(C6H4Me-p)2-Cl2(PEt3)2]. The 31P-{1H} n.m.r. spectra of the complexes have been recorded, and are used extensively in the identification of products.

Generation and interconversions of the di- and tri-nuclear platinum complexes [Pt2H2(dppe)2], [Pt2H3(dppe)2]+, and [Pt3H3(dppe)3]+. Crystal and molecular structure of [Pt3H3(dppe)3]+[BEt4]–, (dppe = Ph2PCH2CH2PPh2)

Multinuclear n.m.r. and crystallographic studies on [Pt2H2(dppe)2], [Pt2H3(dppe)2]+, and [Pt3H3(dppe)3]+ are described, the structure of the latter being unambiguously established for the first time.

Structure and dynamics of hindered organosilicon compounds. The conformations of symmetrical (Me3Si)3C and (PhMe2Si)3C derivatives

Abstract At low temperatures the methyl region of the 1 H and 13 C NMR spectra of (Me 3 Si) 3 CSiCl 3 and the 1 H NMR spectrum of (Me 3 Si) 3 CSiBr 3 each show three signals of equal intensity and the 29 SiNMR spectrum of the trichloride shows only one Me 3 Si signal. These data are consistent with the methyls within each Me 3 Si group becoming inequivalent. Compounds containing the (PhMe 2 Si) 3 C group are able to adopt different conformations at low temperature; in (PhMe 2 Si) 3 CSiCl 3 the phenyl groups mesh together while in (PhMe 2 Si) 3 CBr they are separated by methyl groups. These different arrangements of the ligand can readily be distinguished by 1 H NMR spectroscopy, and the conformation in the case of (PhMe 2 Si) 3 CSiCl 3 has been confirmed in the solid state by X-ray crystallography.

Synthesis and 31P n.m.r. spectroscopy of platinum and palladium complexes containing side-bonded diphenyldiphosphene. The X-ray crystal and molecular structure of [Pd(PhPpph){bis(diphenyl-phosphino)ethane}]

The structure of [Pd(PhPPPh)(dppe)], dppe = bis(diphenylphosphino)ethane, obtained by a new and potentially general synthesis, is essentially plannar with only a 3° twist between the PdP2 planes and a P–P bond distance of 2.121(4)A; 31P n.m.r. data on the analogous platinum complexes show very small s-character in the Pt–P(diphosphene) bonds, suggesting that the structure is essentially a diphosphene bound to Pto rather that of a diphosphido(2–)ligand bound to PtII.

The nature of the co-ordinate link. Part 11. Synthesis and phosphorus-31 nuclear magnetic resonance spectroscopy of platinum and palladium complexes containing side-bonded (E)-diphenyldiphosphene. X-Ray crystal and molecular structures of [Pd{(E)-PhPPPh}(Ph2PCH2CH2PPh2)] and [Pd{[(E)-PhPPPh][W(CO)5]2}(Ph2PCH2CH2PPh2)]

The complexes cis-[MCl2L2] react with Li2(PhPPPh) to give [M(PhPPPh)L2][M = Pd, L2= 1,2-bis(diphenylphosphanyl)ethane (dppe), (1); M = Pt, L2= dppe or (PPh3)2]. Complex (1) reacts with [W(CO)5(thf)](thf = tetrahydrofuran) to give [Pd{(PhPPPh)[W(CO)5]2}(dppe)](2). Complexes were characterized by 31P-{1H} n.m.r. spectroscopy. X-Ray crystal-structure determinations of complexes (1) and (2) reveal nearly identical and planar PdP4 moieties comprising the donor atoms of L2 and η2-[(E)-diphenyldiphosphene] ligands. In (2) the two diphosphene lone pairs co-ordinate to W(CO)5 groups and the W–P bonds are bent 32° away from the Pd atom. The diphosphene P–P bond in (2)[2.186(6)A] is 0.06 A longer than that in (1)[2.121 (4)A], which is similar to that in other diphosphene complexes and is approximately mid-way between the P–P single and double bond lengths. Small values of the coupling constants 1J(PtP) and 2J(PP) involving the diphosphene ligand indicate that the diphosphene uses electrons of low s character in η2-co-ordination.

Dynamic stereochemistry of cis-[PtH(SiR3)(PPh3)2]. Spontaneous ligand interchange with retentilon of nuclear spin–spin correlation

Above 0 °C in various solvents the complexes cis-[PtH(SiR3)(PPh3)2] with R = C6H5, p-ClC6H4, or p-MeC6H4 undergo spontaneous interchange of the PPh3 ligand position by a mechanism which retains P ⋯(Pt)⋯ H spin correlation and is thus intramolecular and non-dissociative within the limits of the n.m.r. experiment.

Novel insertion of [M(PR3)2] fragments (M = Pd, Pt) into the strained phosphorus–carbon bond of the phosphirene complex [W(CO)5(PhPC2Ph2)]. Crystal and molecular structure of [PtW(CO)5(PEt3)2(PhPC2Ph2)]

The striain phosphirene ring in [W(CO)5(PhPC2Ph2)] readily undergoes insertion of [M(PR3)2] fragments (M = Pd, Pt) to give complexes in which phosphorus bridges two different metal atoms.