Synthesis and structural characterisation of group 10 metal(II) gallyl complexes: analogies with platinum diboration catalysts?

Reactions of the anionic gallium(i) heterocycle, [:Ga{[N(Ar)C(H)](2)}](-) (Ar = C(6)H(3)Pr(i)(2)-2,6), with a variety of mono- and bidentate phosphine, tmeda and 1,5-cyclooctadiene (COD) complexes of group 10 metal dichlorides are reported. In most cases, salt elimination occurs, affording either mono(gallyl) complexes, trans-[MCl{Ga{[N(Ar)C(H)](2)}}(PEt(3))(2)] (M = Ni or Pd) and cis-[PtCl{Ga{[N(Ar)C(H)](2)}}(L)] (L = R(2)PCH(2)CH(2)PR(2), R = Ph (dppe) or cyclohexyl (dcpe)), or bis(gallyl) complexes, trans-[M{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)] (M = Ni, Pd or Pt), cis-[Pt{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)], cis-[M{Ga{[N(Ar)C(H)](2)}}(2)(L)] (M = Ni, Pd or Pt; L = dppe, Ph(2)CH(2)PPh(2) (dppm), tmeda or COD). The crystallographic and spectroscopic data for the complexes show that the trans-influence of the gallium(i) heterocycle lies in the series, B(OR)(2) > H(-) > PR(3) approximately [:Ga{[N(Ar)C(H)](2)}](-) > Cl(-). Comparisons between the reactivity of one complex, [Pt{Ga{[N(Ar)C(H)](2)}}(2)(dppe)], with that of closely related platinum bis(boryl) complexes indicate that the gallyl complex is not effective for the catalytic or stoichiometric gallylation of alkenes or alkynes. The phosphaalkyne, Bu(t)C[triple bond, length as m-dash]P, does, however, insert into one gallyl ligand of the complex, leading to the novel, crystallographically characterised P,N-gallyl complex, [Pt{Ga{[N(Ar)C(H)](2)}}{Ga{PC(Bu(t))C(H)[N(Ar)]C(H)N(Ar)}}(dppe)]. An investigation into the mechanism of this insertion reaction has been undertaken.     

Synthesis, characterization, and reactivity of trans-[PtCl(R'R'SO)(A)2]NO3 (R'R'SO = Me2SO, MeBzSO, MePhSO; A= NH3, py, pic). Crystal structure of trans-[PtCl(Me2SO)(py)2]+

Trans complexes such as trans-[PtCl(2)(NH(3))(2)] have historically been considered therapeutically inactive. The use of planar ligands such as pyridine greatly enhances the cytotoxicity of the trans geometry. The complexes trans-[PtCl(R'R'SO)(A)(2)]NO(3) (R'R'SO = substituted sulfoxides such as dimethyl (Me(2)SO), methyl benzyl (MeBzSO), and methyl phenyl sulfoxide (MePhSO) and A = NH(3), pyridine (py) and 4-methylpyridine or picoline (pic)) were prepared for comparison of the chemical reactivity between ammine and pyridine ligands. The X-ray crystal structure determination for trans-[PtCl(Me(2)SO)(py)(2)]NO(3) confirmed the geometry with S-bound Me(2)SO. The crystals are orthorhombic, space group P2(1)2(1)2(1), with cell dimensions a = 7.888(2) A, b = 14.740(3) A, c =15.626(5) A, and Z = 4. The geometry around the platinum atom is square planar with l(Pt-Cl) = 2.304(4) A, l(Pt-S) = 2.218(5) A, and l(Pt-N) = 2.03(1) and 2.02(1) A. Bond angles are normal with Cl-Pt-S = 177.9(2) degrees, Cl-Pt-N(1) = 88.0(4) degrees, Cl-Pt-N(2) = 89.3(5) degrees, S-Pt-N(1) = 93.8(4) degrees, S-Pt-N(2) = 88.9(4) degrees, and N(1)-Pt-N(2) = 177.2(6) degrees. The intensity data were collected with Mo Kalpha radiation with lambda = 0.710 69 A. Refinement was by full-matrix least-squares methods to a final R value of 3.80%. Unlike trans-[PtCl(2)(NH(3))(2)], trans-[PtCl(2)(A)(2)] (A = py or pic) complexes do not react with Me(2)SO. The solvolytic products of cis-[PtCl(2)(A)(2)] (A = py or pic) were characterized. Studies of displacement of the sulfoxide by chloride were performed using HPLC. The sulfoxide was displaced faster for the pyridine complex relative to the ammine complex. Chemical studies comparing the reactivity of trans-[PtCl(R'R'SO)(amine)(2)]NO(3) with a model nucleotide, guanosine 5'-monophosphate (GMP), showed that the reaction gave two principal products: the species [Pt(R'R'SO)(amine)(2)(N7-GMP)], which reacts with a second equivalent of GMP, forming [Pt(amine)(2)(N7-GMP)(2)]. The reaction pathways were different, however, for the pyridine complexes in comparison to the NH(3) species, with sulfoxide displacement again being significantly faster for the pyridine case.     

Chelating or bridging Pd(II) and Pt(II) metalloligands from the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine. New heterometallic Pd(II)/Pt(II) and Pt(II)/Au(I) complexes

The reaction of two equivalents of the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine Ph2PNHC=NNCHS (2) with [PdCl2(NCPh)2] in the presence of NEt3 gives the neutral, P,N-chelated complex cis-[Pd(Ph2PN=CNN=CHS)2] ([Pd(2-H)2], 3b), which is analogous to the Pt(II) analogue cis-[Pt (Ph2PN=CNN=CHS)2] ([Pt(2-H)2], 3a) reported previously. These complexes function as chelating metalloligands when further coordinated to a metal through each of the CH-N atoms. In the resulting complexes, each endo-cyclic N donor of the thiadiazole rings is bonded to a different metal centre. Thus, the heterodinuclear palladium/platinum complexes cis-[Pt(Ph2PN=CNN=CHS)2PdCl2]([Pt(2-H)2·PdCl2], 4a) and cis-[Pd(Ph2PN=CNN=CHS)2PtCl2]([Pd(2-H)2·PtCl2], 4b) were obtained by reaction with [PdCl2(NCPh)2] and [PtCl2(NCPh)2], respectively. In contrast, reaction of 3a with [AuCl(tht)] occurred instead at the P-bound N atom, and afforded the platinum/digold complex cis-[Pt{Ph2PN(AuCl)=CNN=CHS}2] ([Pt(2-H)2(AuCl)2], 5). For comparison, reaction of 4a with HBF4 yielded cis-[Pt(Ph2PNH=CNN=CHS)2PdCl2](BF4)2([H24a](BF4)2, 6), in which the chelated PdCl2 moiety is retained. Complexes 3b, 4a·CH2Cl2, 4b·0.5C7H8, 5·4CHCl3 and 6 have been structurally characterized by X-ray diffraction.     

Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Ir: C-H and N-H activation and catalytic transfer hydrogenation

Chelating amine and amido complexes of late transition metals are highly valuable bifunctional catalysts in organic synthesis, but complexes of bidentate amine-NHC and amido-NHC ligands are scarce. Hence, we report the reactions of a secondary-amine functionalised imidazolium salt 2a and a primary-amine functionalised imidazolium salt 2b with [(p-cymene)RuCl(2)](2) and [Cp*MCl(2)](2) (M = Rh, Ir). Treating 2a with [Cp*MCl(2)](2) and NaOAc gave the cyclometallated compounds Cp*M(C,C)I (M = Rh, 3; M = Ir, 4), resulting from aromatic C-H activation. In contrast, treating 2b with [(p-cymene)RuCl(2)](2), Ag(2)O and KI gave the amine-NHC complex [(p-cymene)Ru(C,NH(2))I]I (5). The reaction of 2b with [Cp*MCl(2)](2) (M = Rh, Ir), NaO(t)Bu and KI gave the amine-NHC complex [Cp*Rh(NH(2))I]I (6) or the amido-NHC complex Cp*Ir(C,NH)I (7); both protonation states of the Ir complex could be accessed: treating 7 with trifluoroacetic acid gave the amine-NHC complex [Cp*Ir(C,NH(2))I][CF(3)CO(2)] (8). These are the first primary amine- or amido-NHC complexes of Rh and Ir. Solid-state structures of the complexes 3-8 have been determined by single crystal X-ray diffraction. Complexes 5, 6 and 7 are pre-catalysts for the catalytic transfer hydrogenation of acetophenone to 1-phenylethanol, with ruthenium complex 5 demonstrating especially high reactivity.     

Simple preparations of Pd6Cl12, Pt6Cl12, and Qn[Pt2Cl8+n], n=1, 2 (Q=TBA+, PPN+) and structural characterization of [TBA][Pt2Cl9] and [PPN]2[Pt2Cl10].C7H8

The hexanuclear Pd6Cl12, i.e., the crystal phase classified as beta-PdCl2, was obtained by reacting [TBA]2[Pd2Cl6] with AlCl3 (or FeCl3) in CH2Cl2. The action of AlCl3 on PtCl42-, followed by digestion of the resulting solid in 1,2-C2H4Cl2 (DCE), CHCl3, or benzene, produced Pt6Cl12.DCE, Pt6Cl12.CHCl3, or Pt6Cl12.C6H6, respectively. Treating [TBA]2[PtCl6] with a slight excess of AlCl3 afforded [TBA][Pt2Cl9], whose anion was established crystallographically to be constituted by two "PtCl6" octahedra sharing a face. Dehydration of H2PtCl6.nH2O with SOCl2 gave an amorphous compound closely analyzing as PtCl4, reactive with [Q]Cl in SOCl2 to yield [Q][Pt2Cl9] or [Q]2[Pt2Cl10], depending on the [Q]Cl/Pt molar ratio (Q=TBA+, PPN+). A single-crystal X-ray diffraction study has shown [PPN]2[Pt2Cl10].C7H8 to contain dinuclear anions formed by two edge-sharing PtCl6 octahedra.     

Stereoselective preparation, structures, and reactivities of phosphine-bridged mixed-metal trinuclear and pentanuclear complexes with tris[2-(diphenylphosphino)ethyl]phosphine

The phosphine-bridged linear trinuclear and pentanuclear complexes with Pd(II)-Pt(II)-Pd(II), Ni(II)-Pt(II)-Ni(II), and Rh(III)-Pd(II)-Pt(II)-Pd(II)-Rh(III) metal-ion sequences were almost quantitatively formed by the stepwise phosphine-bridging reaction of the terminal phosphino groups of tris[2-(diphenylphosphino)ethyl]phosphine (pp3), which is the tetradentate bound ligand of the starting Pd(II) and Ni(II) complexes. The solid-state structures of the trinuclear complexes were determined by X-ray structural analyses, and the structures of the polynuclear complexes in solution were characterized by NMR spectroscopy. The trans and cis isomers of the trinuclear and pentanuclear complexes, which arise from the geometry around the Pt(II) center, were selectively obtained simply by changing the counteranion of the starting complexes: the tetrafluoroborate salts, [MX(pp3)](BF4) [M = Pd(II) or Ni(II), X = Cl- or 4-chlorothiophenolate (4-Cltp-)], gave only the trans isomers, and the chloride salt, [PdCl(pp3)]Cl, gave only the cis isomers. The formation of the trinuclear complex with the 4-Cltp- and chloro ligands, trans-[Pt(4-Cltp)2{PdCl(pp3)}2](BF4)2, proceeded with exchange between the thiolato ligand in the starting Pd(II) complex, [Pd(4-Cltp)(pp(3))](BF4), and the chloro ligands in the starting Pt(II) complex, trans-[PtCl2(NCC6H5)2], retaining the trans geometry around the Pt(II) center. In contrast, the formation reaction between [PdCl(pp3)]Cl and trans-[PtCl2(NCC6H5)2] was accompanied by the trans-to-cis geometrical change on the Pt(II) center to give the trinuclear complex, cis-[PtCl2{PdCl(pp3)}2]Cl2. The mechanisms of these structural conversions during the formation reactions were elucidated by the 31P NMR and absorption spectral changes. The differences in the catalytic activity for the Heck reaction were discussed in connection with the bridging structures of the polynuclear complexes in the catalytic cycle.     

Synthesis, structure, and luminescence of di- and trinuclear palladium/gold and platinum/gold complexes with (2,7-di-tert-butylfluoren-9-ylidene)methanedithiolate

Acetone solutions of [Au(OClO3)(PCy3)] react with complexes [M{S2C=(t-Bu-fy)}2]2- [t-Bu-fy=2,7-di-tert-butylfluoren-9-ylidene; M=Pd (2a), Pt (2b)] or [M{S2C=(t-Bu-fy)}(dbbpy)] [dbbpy=4,4'-di-tert-butyl-2,2'-bipyridyl; M=Pd (3a), Pt (3b)] to give the heteronuclear complexes [M{S2C=(t-Bu-fy)}2{Au(PCy3)}2] [2:1 molar ratio; M=Pd (4a), Pt (4b)], [M{S2C=(t-Bu-fy)}(dbbpy){Au(PCy3)}]ClO4 [1:1 molar ratio; M=Pd (5a), Pt (5b)], or [M{S2C=(t-Bu-fy)}(dbbpy){Au(PCy3)}2](ClO4)2 [2:1 molar ratio; M=Pd (6a), Pt (6b)]. The crystal structures of 3a, 4a, 4b, 5b, and 6a have been solved by single-crystal X-ray studies and, in the cases of the heteronuclear derivatives, reveal the formation of short Pd...Au or Pt...Au metallophilic contacts in the range of 3.048-3.311 A. Compounds 4a and b and 5a and b undergo a dynamic process in solution that involves the migration of the [Au(PCy3)]+ units between the sulfur atoms of the dithiolato ligands. The coordination of 2a and b and 3a and b to [Au(PCy3)]+ units results in important modifications of their photophysical properties. The dominant effect in the absorption spectra is an increase in the energy of the MLCT (4a and b) or charge transfer to diimine (5a, b, 6a, b) transitions because of a decrease in the energies of the mixed metal/dithiolate HOMOs. The Pd complexes 2a and 4a are luminescent at 77 K, and the features of their emissions are consistent with an essentially metal-centered 3d-d state. The Pt/Au complexes are also luminescent at 77 K, and their emissions can be assigned as originating from a MLCT triplet state (4b) or a mixture of charge transfer to diimine and diimine intraligand pi-pi* triplet states (5b and 6b).     

Mononuclear (Pd, Pt), heterodinuclear (PdAg, PtAg), and tetranuclear (Pd2Ag2, Pt2Ag2) 1,1-ethylenedithiolato complexes

lp;&-5q;1 The reactions of [Tl2[S2C=C[C(O)Me]2]]n with [MCl2L2] (1:1) or with [MCl2(NCPh)2] and PPh3 (1:1:2) give complexes [M[eta2-S2C=C[C(O)Me]2]L2] [M = Pt, L2 = 1,5-cyclooctadiene (cod) (1); L2 = bpy, M = Pd (2a), Pt (2b), L = PPh3, M = Pd (3a), Pt (3b)] whereas with MCl2 and QCl (2:1:2) anionic derivatives Q2[M[eta2-S2C=C[C(O)Me]2]2] [M = Pd, Q = NMe4 (4a), Ph3P=N=PPh3 (PPN) (4a'), M = Pt, Q = NMe4 (4b)] are produced. Complexes 1 and 3 react with AgClO4 (1:1) to give tetranuclear complexes [[ML2]2Ag2[mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2]](ClO4)2 [L = PPh3, M = Pd (5a), Pt (5b), L2 = cod, M = Pt (5b')], while the reactions of 3 with AgClO4 and PPh3 (1:1:2) give dinuclear [[M(PPh3)2][Ag(PPh3)2][mu2,eta2-(S,S')-S2C=C[C(O)Me]2]]]ClO4 [M = Pd (6a), Pt (6b)]. The crystal structures of 3a, 3b, 4a, and two crystal forms of 5b have been determined. The two crystal forms of 5b display two [Pt(PPh3)2][mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2] moieties bridging two Ag(I) centers.     

The preparation and characterisation of hetero- and homobimetallic complexes containing bridging naphthalene-1,8-dithiolato ligands

Homo- and heterobimetallic complexes of the form [(PPh(3))(2)(mu(2)-1,8-S(2)-nap){ML(n)}] (in which (1,8-S(2)-nap)=naphtho-1,8-dithiolate and {ML(n)}={PtCl(2)} (1), {PtClMe} (2), {PtClPh} (3), {PtMe(2)} (4), {PtIMe(3)} (5) and {Mo(CO)(4)} (6)) were obtained by the addition of [PtCl(2)(NCPh)(2)], [PtClMe(cod)] (cod=1,5-cyclooctadiene), [PtClPh(cod)], [PtMe(2)(cod)], [{PtIMe(3)}(4)] and [Mo(CO)(4)(nbd)] (nbd=norbornadiene), respectively, to [Pt(PPh(3))(2)(1,8-S(2)-nap)]. Synthesis of cationic complexes was achieved by the addition of one or two equivalents of a halide abstractor, Ag[BF(4)] or Ag[ClO(4)], to [{Pt(mu-Cl)(mu-eta(2):eta(1)-C(3)H(5))}(4)], [{Pd(mu-Cl)(eta(3)-C(3)H(5))}(2)], [{IrCl(mu-Cl)(eta(5)-C(5)Me(5))}(2)] (in which C(5)Me(5)=Cp*=1,2,3,4,5-pentamethylcyclopentadienyl), [{RhCl(mu-Cl)(eta(5)-C(5)Me(5))}(2)], [PtCl(2)(PMe(2)Ph)(2)] and [{Rh(mu-Cl)(cod)}(2)] to give the appropriate coordinatively unsaturated species that, upon treatment with [(PPh(3))(2)Pt(1,8-S(2)-nap)], gave complexes of the form [(PPh(3))(2)(mu(2)-1,8-S(2)-nap){ML(n)}][X] (in which {ML(n)}[X]={Pt(eta(3)-C(3)H(5))}[ClO(4)] (7), {Pd(eta(3)-C(3)H(5))}[ClO(4)] (8), {IrCl(eta(5)-C(5)Me(5))}[ClO(4)] (9), {RhCl(eta(5)-C(5)Me(5))}[BF(4)] (10), {Pt(PMe(2)Ph)(2)}[ClO(4)](2) (11), {Rh(cod)}[ClO(4)] (12); the carbonyl complex {Rh(CO)(2)}[ClO(4)] (13) was formed by bubbling gaseous CO through a solution of 12. In all cases the naphtho-1,8-dithiolate ligand acts as a bridge between two metal centres to give a four-membered PtMS(2) ring (M=transition metal). All compounds were characterised spectroscopically. The X-ray structures of 5, 6, 7, 8, 10 and 12 reveal a binuclear PtMS(2) core with PtM distances ranging from 2.9630(8)-3.438(1) A for 8 and 5, respectively. The napS(2) mean plane is tilted with respect to the PtP(2)S(2) coordination plane, with dihedral angles in the range 49.7-76.1 degrees and the degree of tilting being related to the PtM distance and the coordination number of M. The sum of the Pt(1)coordination plane/napS(2) angle, a, and the Pt(1)coordination plane/M(2)coordination plane angle, b, a+b, is close to 120 degrees in nearly all cases. This suggests that electronic effects play a significant role in these binuclear systems.     

Bis(isothiocyanato)bis(phosphine) complexes of group 10 metals: reactivity toward organic isocyanides

Treatment of Ni(NCS)2(PMe2Ph)2 with organic isocyanides CN-R gave five-coordinate isocyanide Ni(II) complexes, Ni(CN-R)(NCS)2(PMe2Ph)2 (R = C6H3-2,6-Me2 (1), t-Bu (2)). Interestingly, the corresponding reaction of Ni(NCS)2(P(n-Pr)3)2 with 2 equiv. of CN-t-Bu gave an unusual compound, which exists as an ion pair of the trigonal bipyramidal cation [Ni(P(n-Pr)3)2(CN-t-Bu)3]2+ (3) and the dinuclear NCS-bridged anion [Ni(1,3-micro-NCS)(NCS)3]2(2-) (4). In contrast, Pd(NCS)2(P(n-Pr)3)2 underwent substitution with 2 equiv. of CN-t-Bu to give the four-coordinate mono(isocyanide) Pd(II) complex Pd(NCS)(SCN)(CN-t-Bu)(P(n-Pr)3) (5) via phosphine dissociation. Reactions of M(NCS)2L2 (M = Pd, Pt; L = PMe3, PEt3, PMePh2, P(n-Pr)3) with two equiv. of CN-R (R = t-Bu, i-Pr, C6H3-2,6-Me2) gave the corresponding bis(isocyanide) complexes [M(CN-R)2(PR3)2](SCN)2 (7-13), except for Pd(NCS)2(PEt3)2 that reacted with CN-R' (R' = i-Pr, C6H3-2,6-Me2) and produced the mono(isocyanide) Pd(II) complexes [Pd(CN-R')(SCN)(PEt3)2](SCN) (14 and 15). Finally, treatment of M(NCS)2(PMe3)2 (M = Ni, Pd, Pt) with sterically bulky isocyanide CN-C6H3-2,6-i-Pr2 gave various products, (16-18) depending on the identity of the metal.     

Pop-the-cork strategy in synthetic utilization of imines: stabilization by complexation and activation via liberation of the ligated species

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with ethanol allowed the isolation of trans-[PtCl(4)[E-NH[double bond]C(R)OEt](2)]. The latter were reduced selectively, by the ylide Ph(3)P[double bond]CHCO(2)Me, to trans-[PtCl(2)[E-NH[double bond]C(R)OEt](2)]. The complexed imino esters NH[double bond]C(R)OEt were liberated from the platinum(II) complexes by reaction with 2 equiv of 1,2-bis(diphenylphosphino)ethane (dppe) in chloroform; the cationic complex [Pt(dppe)(2)]Cl(2) precipitates almost quantitatively from the reaction mixture and can be easily separated by filtration to give a solution of NH[double bond]C(R)OEt with a known concentration of the imino ester. The imino esters efficiently couple with the coordinated nitriles in trans-[PtCl(4)(EtCN)(2)] to give, as the dominant product, [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] containing a previously unknown linkage, i.e., ligated N-(1-imino-propyl)-alkylimidic acid ethyl esters. In addition to [PtCl(4)[NH[double bond]C(Et)N[double bond]C(Et)OEt](2)], another compound was generated as the minor product, i.e., [PtCl(4)(EtCN)[NH[double bond]C(Et)N[double bond]C(Et)OEt]], which was reduced to [PtCl(2)(EtCN)[NH[double bond]C(Et)N[double bond]C(Et)OEt]], and this complex was characterized by X-ray single-crystal diffraction. The platinum(IV) complexes [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] are unstable toward hydrolysis and give EtOH and the acylamidine complexes trans-[PtCl(4)[Z-NH[double bond]C(Et)NHC(R)[double bond]O](2)], where the coordination to the Pt center results in the predominant stabilization of the imino tautomer NH[double bond]C(Et)NHC(R)[double bond]O over the other form, i.e., NH(2)C(Et)[double bond]NC(R)[double bond]O, which is the major one for free acylamidines. The structures of trans-[PtCl(4)[Z-NH[double bond]C(Et)NHC(R)[double bond]O](2)] (R = Me, Et) were determined by X-ray studies. The complexes [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] were reduced to the appropriate platinum(II) compounds [PtCl(2)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)], which, similarly to the appropriate Pt(IV) compounds, rapidly hydrolyze to yield the acylamidine complexes [PtCl(2)[NH[double bond]C(Et)NHC(R)[double bond]O](2)] and EtOH. The latter acylamidine compounds were also prepared by an alternative route upon reduction of the corresponding platinum(IV) complexes. Besides the first observation of the platinum(IV)-mediated nitrile-imine ester integration, this work demonstrates that the application of metal complexes gives new opportunities for the generation of a great variety of imines (sometimes unreachable in pure organic chemistry) in metal-mediated conversions of organonitriles, the "storage" of imino species in the complexed form, and their synthetic utilization after liberation.     

Metallochain cluster complexes and metallomacrocyclic triangles based on coordination bonds between palladium or platinum and diphosphinoacetylene ligands

To explore the potential of the coordination chemistry of Pd and Pt halides with phosphinoacetylene ligands for the generation of novel, highly metallated organometallic coordination polymers, investigations on model compounds [MX2(PPh2 C identical to CPh)2] that exhibit trans-configured Pd centers and cis-configured Pt centers have been performed. The molecular structure of the trans-Pd complexes 2 (M = Pd, X = Br) and 5 (M = Pd, X = I) appeared suitable for the generation of linear materials, whereas the cis-Pt complex 6 (M = Pt, X = I) suggested the prospective formation of ring systems. The presence of acetylene moieties allowed for further increase of metal concentration by cluster formation with [Co2(CO)8]. Two novel bimetal cluster complexes 7 and 8 were obtained from 5 and 6, respectively, and these exhibit a bridging iodine ligand as an interesting structural motif leading to heterocyclic systems with M-I-Co-C-P skeletons (M = Pd or Pt). A similar approach with [Fe2(CO)9] led to the formation of several products, including an unusual Pd-Fe cluster-containing compound 10. The extension of the coordination strategy to rigid bis(phosphinoacetylene) ligands gave rise to strained ring systems. Surprisingly, for the cis-configured PtCl2 center, a rarely observed triangular structure 12 was obtained exclusively. The corresponding PtI2 analog, 13a rearranged over time to form a "ring-fused" system 13b with an extended BINAP-like ligand.     

Pincer-like amido complexes of platinum, palladium, and nickel

The ligands bis(8-quinolinyl)amine (BQAH, 1), (2-pyridin-2-yl-ethyl)-(8-quinolinyl)amine (2-pyridin-2-yl-ethyl-QAH, 2), o-dimethylaminophenyl(8-quinolinyl)amine (o-(NMe2)Ph-QAH, 3), and 3,5-dimethylphenyl(8-quinolinyl)amine (3,5-Me2Ph-QAH, 4) have been prepared in high yield from aryl halide and amine precursors by palladium-catalyzed coupling reactions. Deprotonation of 1 with nBuLi in toluene affords the lithium amide complex [Li][BQA] (5), whose dimeric solid-state crystal structure is presented. Lithium amide 5 was transmetalated by TlOTf to afford the thallium(I) amido complex [Tl][BQA] (6). An X-ray structural study of 6 shows it to be a 1:1 complex of the BQA ligand and Tl. Entry into the group 10 chemistry of the parent ligand 1 was effected by both protolytic and metathetical strategies. Thus, the divalent chloride complexes (BQA)PtCl (7), (BQA)PdCl (8), and (BQA)NiCl (9) were prepared and fully characterized. An X-ray structural study for each of these three complexes shows them to be well-defined, square-planar complexes in which the auxiliary BQA ligand binds in a planar, eta(3)-fashion. For comparison, the reactivity of ligands 2-4 with (COD)PtCl2 was studied. While reaction with ligand 2 afforded an ill-defined product mixture, ligands 3 and 4 reacted with (COD)PtCl2 to generate the unusual alkyl complexes (o-(NMe2)Ph-QA)Pt(1,2-eta(2)-6-sigma-cycloocta-1,4-dienyl) (10) and (3,5-Me2Ph-QA)Pt(1,2-eta(2)-6-sigma-cycloocta-1,4-dienyl) (11), both of which have been structurally characterized.     

(Fluoren-9-ylidene)methanedithiolato complexes of platinum: synthesis, reactivity, and luminescence

Platinum(II) complexes with (fluoren-9-ylidene)methanedithiolato and its 2,7-di-tert-butyl- and 2,7-dimethoxy-substituted analogues were obtained by reacting different chloroplatinum(II) precursors with the piperidinium dithioates (pipH)[(2,7-R2C12H6)CHCS2] [R = H (1a), t-Bu (1b), or OMe (1c)] in the presence of piperidine. The anionic complexes Q2[Pt{S(2)C=C(C12H6R(2)-2,7)}2] [R = H, (Pr(4)N)(2)2a; R = t-Bu, (Pr4N)(2)2b, (Et4N)(2)2b; R = OMe, (Pr4N)(2)2c] were prepared from PtCl(2), piperidine, the corresponding QCl salt, and 1a-c in molar ratio 1:2:2:2. In the absence of QCl, the complexes (pipH)(2)2b and [Pt(pip)(4)]2b were isolated depending on the PtCl(2):pip molar ratio. The neutral complexes [Pt{S2C=C(C12H6R(2)-2,7)L(2)] [L = PPh(3), R = H (3a), t-Bu (3b), OMe (3c); L = PEt(3), R = H (4a), t-Bu (4b), OMe (4c); L(2) = dbbpy, R = H (5a), t-Bu (5b), OMe (5c) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridyl)] were similarly prepared from the corresponding precursors [PtCl2L2] and 1a-c in the presence of piperidine. Oxidation of Q(2)2b with [FeCp2]PF6 afforded the mixed Pt(II)-Pt(IV) complex Q2[Pt2{S2C=C[C12H6(t-Bu)(2)-2,7]}4] (Q(2)6, Q = Et4N+, Pr4N+). The protonation of (Pr4N)(2)2b with 2 equiv of triflic acid gave the neutral dithioato complex [Pt2{S2CCH[C12H6(t-Bu)(2)-2,7]}4] (7). The same reaction in 1:1 molar ratio gave the mixed dithiolato/dithioato complex Pr4N[Pt{S2C=C[C12H6(t-Bu)(2)-2,7]}{S2CCH[C12H6(t-Bu)(2)-2,7]}] (Pr(4)N8) while the corresponding DMANH+ salt was obtained by treating 7 with 2 equiv of 1,8-bis(dimethylamino)naphthalene (DMAN). The crystal structures of 3b and 5c.CH2Cl2 have been solved by X-ray crystallography. All the platinum complexes are photoluminescent at 77 K in CH2Cl2 or KBr matrix, except for Q(2)6. Compounds 5a-c and Q8 show room-temperature luminescence in fluid solution. The electronic absorption and emission spectra of the dithiolato complexes reveal charge-transfer absorption and emission energies which are significantly lower than those of analogous platinum complexes with previously described 1,1-ethylenedithiolato ligands and in most cases compare well to those of 1,2-dithiolene complexes.     

Siloxane-supported organometallic compounds and their catalytic activities for the hydrosilylation of vinylsilanes and dienes

Two different classes of silicone-modified ligands were prepared: nitrile derivatives, 4'-[3-(organosilyl)propoxy]biphenyl-4-carbonitrile R'3SiC3H6OC6H4C6H4CN (R'3Si- = a: Me3SiOSiMe2-, b: (Me(3)SiO)2SiMe-, c: Me3SiO(Me2SiO)3SiMe2-, d: Me3SiO(Me2SiO)25SiMe2-); and, pyridine derivatives, isonicotinic acid 2-methoxy-4-[3-(organosilyl)propyl]phenyl ester R'3SiC3H6Ph(O)MeOCOC5H4N . Compounds and were bound to Pd and Pt using ligand substitution reactions with organometallic precursors to give (R3SiC3H6OC6H4C6H4CN)2PdCl2, (R3SiC3H6OC6H4C6H4CN)2PtCl2 and (R3SiC3H6C6H3(OMe)OC(O)C5H4N)PtCl2(eta(2)-1-octene). The polydimethylsiloxane (PDMS)-supported Pt and Pd compounds and had excellent solubility in both organic solvents and polysiloxanes. All the Pt compounds exhibited good catalytic activity for hydrosilylation of vinylsilanes. The PDMS-supported Pd compound also was effective catalyst for hydrosilylation of a diene, isoprene, with 1,1,1,3,3-pentamethyldisiloxane MM(H) to produce the 1,4-adduct Me3SiOSiMe2CH2CH=CMeCH2-H as a major product.     

Special effects of ortho-isopropylphenyl groups. Diastereoisomerism in platinum(II) and palladium(II) complexes of helically chiral PAr3 ligands

The coordination chemistry of the four phosphines, P{C6H3(o-CH3)(p-Z)}3 where Z = H (1a) or OMe (1b) and P{C6H3(o-CHMe2)(p-Z)}3 Z = H (1c) or OMe (1d) with platinum(II) and palladium(II) is reported. Mononuclear complexes trans-[PdCl2L2](L = 1a,b) and trans-[PtCl2L2](L = 1a-c) have been prepared and the crystal structures of trans-[PdCl2(1b)2] and trans-[PtCl2(1c)2] as their dichloromethane solvates have been determined. The structures show that in these complexes, the ligands adopt g+ g+ a conformations. Examination of the Cambridge Structural Database confirms this to be one of only two conformer types that tri-o-tolylphosphines adopt and the only viable conformer in 4 and 6 coordinate complexes. The binuclear complexes trans-[Pd2Cl4L2](L = 1c,d) are formed even when an excess of the bulky 1c,d is used in the synthesis and the crystal structure of trans-[Pd2Cl4(1c)2] as its chloroform solvate is reported. Reaction of [PtCl2(NCBu(t))2] with 1b-d in refluxing toluene gave the cycloplatinated species [Pt2Cl2(L - H)2] where L - H is phosphine 1b-d deprotonated at one of the ortho-methyl carbon atoms. Variable temperature 31P and 1H NMR spectroscopy reveals that all the complexes reported are fluxional. The processes are analysed in terms of restricted P-C and P-M rotations that give rise to diastereoisomeric rotamers because of the helically chiral orientations of the aryl substituents. For the complexes of the bulky ligands 1c,d, rotation about the P-C bond is slow on the NMR timescale even up to 75 degrees C. The crystal structure of the cyclometallated complex [Pt2Cl2(1d - H)2] has been determined.     

Synthesis and coordination chemistry of an alkyne functionalised bis(pyrazolyl)methane ligand

The alkyne functionalised bidentate N-donor ligand (2-propargyloxyphenyl)bis(pyrazolyl)methane was prepared in high yield from the reaction of (2-hydroxyphenyl)bis(pyrazolyl)methane with propargyl bromide in the presence of base. A series of transition-metal complexes including [MCl2] (M=Cu, Co, Ni, Zn, Pt), [M2](NO3)2 (M=Cu, Co, Ni, Zn), [Ag]NO3 and [Pd(dppe)](OTf)2 were prepared and characterised by spectroscopic techniques. In addition, ligand as well as the Co(II) and Zn(II) complexes [CoCl2]2, [ZnCl2] were structurally characterized by single-crystal X-ray diffraction. The organometallic gold(I) and platinum(II) acetylide complexes [Pz2CH(C6H(4)-2-OCH2C[triple bond, length as m-dash]CAuPPh3)] and trans-[{Pz2CHC6H(4)-2-OCH2C[triple bond, length as m-dash]C}2Pt(PPh3)2] were prepared from and [AuCl(PPh3)] and trans-[PtCl2(PPh3)2], respectively. Treatment of these complexes with [Pd(OTf)2(dppe)] or [Cu(MeCN)4]PF6 results in formation of the cationic, mixed-metal complexes, which were isolated (Pt/Pd, Au/Pt) or detected by electrospray mass spectrometry (Au/Cu, Pt/Cu).     

Synthesis, molecular structures, and chemistry of some new palladium(II) and platinum(II) complexes with pentafluorophenyl ligands

A series of palladium(II) and platinum(II) complexes possessing pentafluorophenyl ligands of the general formula [M(L-L)(C6F5)Cl][space](M = Pd 3; L-L=tmeda (N,N,N',N',-tetramethylethylenediamine) a; 1,2-bis(2,6-dimethylphenylimino)ethane) b; dmpe (1,2-bis(dimethylphosphino)ethane) c; dcpe (1,2-bis(dicyclohexylphosphino)ethane) d; Pt ; L-L=tmeda a; 1,2-bis[3,5-bis(trifluoromethyl)phenylimino]-1,2-dimethylethane b; dmpe c; dcpe d) were readily synthesized from the dimer [M(C6F5)(tht)(mu-Cl)2] (M=Pd 1b, Pt 2b; tht=tetrahydrothiophene) and the corresponding bidentate ligand. In the case of palladium, the corresponding iodo analogues (6a-c) were readily synthesized in a one-pot reaction from [Pd2(dba)3], iodopentafluorobenzene, and the appropriate ligand. The platinum complexes 4c-d were then converted to the water complexes [Pt(L-L)(C6F5)(OH2)]OTf (L-L =dmpe 7a; dcpe 7b)via reaction with AgOTf in the presence of water. Attempts to convert the palladium complexes 3c-d to the corresponding water complexes resulted in the disproportionation of the intermediate water complex to form [Pd(L-L)(C6F5)2] (L-L=dmpe 8) or [Pd(L-L)2][OTf]2(L-L=dcpe 9). Upon standing in solution for prolonged periods, complex 7a undergoes an identical disproportionation reaction to the Pd analogues to form [Pt(L-L)(C6F5)2] (L-L=dmpe 10). Complexes 4c and 4d were converted to the corresponding hydrides (11b-c, respectively) using two different hydride sources: 11a was formed by the reaction of with NaBH4 in refluxing THF, while 11b was synthesized in near quantitative yield using [Cp2ZrH2] in refluxing THF. Attempts to synthesize eta2-tetrafluorobenzyne complexes [Pt(L-L)(C6F4)] (L-L=dmpe, dcpe) from reaction of 11a-b with butyllithium were unsuccessful. The molecular structures of 3a,4a, 4c, 4d, 6b, 7a, 8, 11b and have been determined by X-ray crystallographic studies, and are discussed.     

The first examples of metal-mediated addition of a phosphorus imine to nitriles; the preparation and X-ray crystal structures of [PtCl4{NH=C(Et)N=PPh3}2] and [PtCl2(EtCN){NH=C(Et)N[double bond, length as m-dash]PPh3}

Imino(triphenyl)phosphorane, Ph3P=NH (1), reacts with nitrile complexes of Pt(IV) to generate hydrolytically sensitive [PtCl4{NH=C(R)N=PPh3}2](R=Me 2a, Et 2b, Ph 2c), and with the Pt(II) complex [PtCl2(EtCN)2] to give [PtCl2(EtCN){NH=C(Et)N=PPh3}](3) and [PtCl2{NH=C(Et)N=PPh3}2](4); X-ray crystallography performed upon (2b) and (3) confirms the presence of an imine/nitrile addition ligand bound by the terminal nitrogen.     

Reduction of (imine)Pt(IV) to (imine)Pt(II) complexes with carbonyl-stabilized phosphorus ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3P=CHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4[NH=C(Me)ON=CR1R2]2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)=NOH], [PtCl4[NH=C(Me)ONR2]2] (R = Me, Et, CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5[NH=C(Me)ON=CR2]] [R2 = Me2, (CH2)4, (CH2)5] and 1 equiv of Ph3P=CHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum center. All thus prepared compounds (excluding previously described Delta4-1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C[1H], 31P[1H] and 195Pt NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2[NH=C(Me)ON=CMe2]2] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) A, c = 15.916(3) A] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) A, b = 12.486(4) A, c = 10.149(3) A]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides Ph3P=CHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV) complexes for biological studies.