Synthesis, structure and photophysical properties of binuclear methylplatinum complexes containing cyclometalating 2-phenylpyridine or benzo{h}quinoline ligands: a comparison of intramolecular Pt-Pt and π-π interactions

The binuclear cyclometalated complexes [Pt(2)Me(2)(ppy)(2)(μ-dppm)], 1a, and [Pt(2)Me(2)(bhq)(2)(μ-dppm)], 1b, in which ppy = 2-phenylpyridyl, bhq = benzo{h}quinoline and dppm = bis(diphenylphosphino)methane, were synthesized by the reaction of [PtMe(SMe(2))(ppy)] or [PtMe(SMe(2))(bhq)] with 1/2 equiv of dppm at room temperature, respectively. Complexes 1a and 1b were fully characterized by multinuclear ((1)H, (31)P, (13)C, and (195)Pt) NMR spectroscopy and were further identified by single crystal X-ray structure determination. A comparison of the intramolecular Pt-Pt and π-π interactions in complexes 1a and 1b has been made on the basis of data on crystal structures and wave functions analysis. The binuclear complexes 1a and 1b are luminescent in the solid state, and showing relatively intense orange-red emissions stemming from (3)MMLCT excited states. The reaction of complex 1b with excess MeI gave the binuclear cyclometalated Pt(IV)-Pt(IV) complex [Pt(2)Me(4)(bhq)(2)(μ-I)(2)], 2. Crystal structure of complex 2 shows intermolecular C-H···I and C-H···π interactions in solid state.     

Organoplatinum complexes containing bis(diphenylphosphino)amine as ligand: uncommon case of N-H . . . I-Pt hydrogen bonding

The complex [PtMe(2)(dppa)], 1a, dppa = Ph(2)PNHPPh(2), which has previously been prepared as a mixture with the dimeric form [Pt(2)Me(4)(micro-dppa)(2)], was synthesized in pure form by the reaction of [PtCl(2)(dppa)] with MeLi. The aryl analogue [Pt(p-MeC(6)H(4))(2)(dppa)], 1b, was prepared by replacement of SMe(2) in cis-[Pt(p-MeC(6)H(4))(2)(SMe(2))(2)] with dppa. The reaction of the chelate complexes 1 with one equiv. of dppa afforded the complexes [PtR(2)(dppa-P)(2)], R=Me, 2a and R=p-MeC(6)H(4) 2b. The reaction of [PtR(2)(dppa)], 1, with neat MeI gave the organoplatinum(iv) complexes [PtR(2)MeI(dppa)], R=Me, 5a and R=p-MeC(6)H(4), 5b. The structure of 5a, determined by X-ray crystallography, indicated that the complex undergoes self-assembly by intermolecular N-H . . . I-Pt hydrogen bonding. MeI was also double oxidatively added to organodiplatinum(ii) complex cis,cis-[Me(2)Pt(micro-SMe(2))(micro-dppa)PtMe(2)], to give diorganoplatinum(iv) complex [Me(3)Pt(micro-dppa)(micro-I)(2)PtMe(3)], 4. The aryl analogue organodiplatinum(ii) complex cis,cis-[(p-MeC(6)H(4))(2)Pt(micro-SMe(2))(micro-dppa)Pt(p-MeC(6)H(4))(2)], 3b, was prepared by the reaction of cis-[Pt(p-MeC(6)H(4))(2)(SMe(2))(2)] with half equiv. of dppa, but 3b refused to react with MeI, probably because of the steric effects of the aryl ligands. The tetramethyl complex [PtMe(4)(dppa)], 6, was prepared either by reaction of 5a with MeLi or by replacement of SMe(2) in [Pt(2)Me(8)(micro-SMe(2))(2)] with dppa. All the complexes were fully characterized in solution by multinuclear NMR ((1)H, (13)C, (31)P and (195)Pt) methods and their coordination compared with that of the corresponding known dppm complexes.     

Selenolate gold complexes with aurophilic Au(I)-Au(I) and Au(I)-Au(III) interactions

The gold(I) selenolate compound [Au(2)(SePh)(2)(mu-dppf)] (dppf = 1,1'-bis(diphenylphosphino)ferrocene) has been prepared by reaction of [Au(2)Cl(2)(mu-dppf)] with PhSeSiMe(3) in a molar ratio 1:2. This complex reacts with gold(I) or gold(III) derivatives to give polynuclear gold(I)-gold(I) or gold(I)-gold(III) complexes of the type [Au(4)(mu-SePh)(2)(PPh(3))(2)(mu-dppf)](OTf)(2), [Au(3)(C(6)F(5))(3)(mu-SePh)(2)(mu-dppf)], or [Au(4)(C(6)F(5))(6)(mu-SePh)(2)(mu-dppf)], with bridging selenolate ligands. The reaction of [Au(2)(SePh)(2)(mu-dppf)] with 1 equiv of AgOTf leads to the formation of the insoluble Ag(SePh) and the compound [Au(2)(mu-SePh)(mu-dppf)]OTf. The complexes [Au(4)(C(6)F(5))(6)(mu-SePh)(2)(mu-dppf)] and [Au(2)(mu-SePh)(mu-dppf)]OTf (two different solvates) have been characterized by X-ray diffraction studies and show the presence of weak gold(I)-gold(III) interactions in the former and intra- and intermolecular gold(I)-gold(I) inter-actions in the later.     

Oxidative addition of methyl iodide to a new type of binuclear platinum(II) complex: a kinetic study

A new organodiplatinum(II) complex cis,cis-[Me2Pt(mu-NN)(mu-dppm)PtMe2] (1), in which NN = phthalazine and dppm = bis(diphenylphosphino)methane, is synthesized by the reaction of cis,cis-[Me2Pt(mu-SMe2)(mu-dppm)PtMe2] with 1 equiv of NN. Complex 1 has a 5d(pi)(Pt) --> pi(imine) metal-to-ligand charge-transfer band in the visible region, which was used to easily follow the kinetics of its reaction with MeI. Meanwhile, the complex contains a robust bridging dppm ligand that holds the binuclear integrity during the reaction. A double MeI oxidative addition was observed, as shown by spectrophotometry and confirmed by a low-temperature 31P NMR study. The classical S(N)2 mechanism was suggested for both steps, and the involved intermediates were suggested. Consistent with the proposed mechanism, the rates of the reactions at different temperatures were slower in benzene than in acetone and large negative deltaS values were found in each step. However, some abnormalities were observed in the related rate constants and deltaS values, which were demonstrated to be due to the associative involvement of the polar acetone molecules in the reactions. The rates are almost 6 times slower in the second step as compared to the first step because of the electronic effects transmitted through the ligands and the steric effects.     

Preparation, properties and structures of the first series of organometallic Pt(II) and Pt(IV) complexes with stibine co-ligands

The planar Pt(II) monomers [PtMe2(L-L)] and [(PtMe2)2(L'-L')2] dimers (L-L = R2Sb(CH2)3SbR2, o-C6H4(CH2SbMe2)2; L'-L' = R2SbCH2SbR2; R = Me or Ph) are obtained in good yield via reaction of [PtMe2(SMe2)2] with L-L or L'-L' in benzene. The Pt(iv) stibines, [PtMe3(L-L)I] (L-L = R2Sb(CH2)3SbR2, o-C6H4(CH2SbMe2)2 or 2 x SbPh3, SbMePh2 or SbMe2Ph) are obtained by treatment of [PtMe3I] with L-L in chloroform. These represent the first series of stable Pt(IV) stibine complexes. All of the products have been characterised by 1H, 13C{1H}, 195Pt NMR spectroscopy, electrospray mass spectrometry and analysis. Crystal structure determinations on [PtMe3{R2Sb(CH2)3SbR2}I], [PtMe3{o-C6H4(CH2SbMe2)2}I] and [PtMe3(SbPh3)2I] confirm the distorted octahedral environment at Pt, with fac Me groups and mutually cis Sb donor atoms. The Sb-Pt-Sb angle in the seven-membered chelate ring of the o-C6H4(CH2SbMe2)2 complex is ca. 96 degrees , compared to <90 degrees in the complexes with six-membered chelates. The C1-distibines R2SbCH2SbR2 afford only the dinuclear [(PtMe3)2(mu-R2SbCH2SbR2)(mu-I)2] in which the stibine ligand and two I atoms bridge two Pt atoms giving an edge sharing bioctahedral geometry which has been confirmed by a crystal structure analysis. The Pt(II) species undergo oxidative addition with MeI to give the corresponding Pt(IV) species, while the Pt(IV) species reductively eliminate ethane upon thermolysis.     

Aryl, methyl-diplatinum complexes each with a metal-metal donor-acceptor bond and bridging 2-diphenylphosphinopyridine (PN) ligands: general synthetic approach and mechanism of isomerization

A general synthetic method has been designed to prepare a series of unsymmetrical cationic organo-diplatinum complexes each containing two bridging 2-diphenylphosphinopyridine (PN), PPh(2)py, ligands and a platinum-platinum donor-acceptor bond. Thus, reaction of cis-[PtR(2)(SMe(2))2] (R = Ph, p-MeC(6)H(4) or p-FC(6)H(4)), 1, or cis,cis-[R(2)Pt(micro-SMe(2))(2)PtR(2)](R = Me) with 2 equiv. or 4 equiv., respectively, of PN in CH(2)Cl(2) gave cis-[PtR(2)(PN-kappa(1)P)(2)], 2. When complex 2 was reacted with 1 equiv. of HX (X = CF(3)COO) in CH(2)Cl(2), an approximately 2 : 1 mixture of trans-[PtRX(PN-kappa(1)P)(2)], 3, and [PtR(eta(2)-PN)(PN-kappa(1)P)]X, 4, was obtained. The reaction of one equiv. of the latter monomeric mixture with 0.5 equiv. of cis,cis-[R'(2)Pt(micro-SMe(2))(2)PtR'(2)] (R' = Me) or one equiv. of cis-[PtR'(2)(SMe(2))(2)] (R' = p-MeC(6)H(4)) in CH(2)Cl(2) immediately gave the head-to-head (HH) stereoisomer of the diplatinum complex hh-[RPt(micro-PN)(2)PtR'(2)]X, 6. However, the same reaction in benzene gave the corresponding head-to-tail (HT) stereoisomer ht-[RPt(micro-PN)(micro-NP)PtR'(2)]X, 9, in pure form after a few hours. The conversion of the HH isomer 6 to the HT isomer 9 in CH(2)Cl(2) took place very slowly during 10 d, while the conversion in C(6)H(6) was much faster and took place over 5 h. Based on the observations, a mechanism for the conversion of the kinetic HH stereoisomer to the thermodynamic HT stereoisomer is suggested which involves association of X- with the N(2)PtR'(2) center following by one-arm dissociation of one of the PN bridging ligands from the nitrogen terminal in the HH isomer, and subsequent exchange of the ligating atom and reformation of the HT arrangement. The methyl-di p-tolyl dimer ht-[MePt(micro-PN)(micro-NP)Pt(p-MeC(6)H(4))(2)]X, 9e, in solution gradually isomerizes to ht-[(p-MeC(6)H(4))Pt(micro-PN)(micro-NP)PtMe(p-MeC(6)H(4))]X, 11, by an aryl ligand transfer. All the complexes were fully characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and the complexes ht-[PhPt(micro-PN)(micro-NP)PtMe(2)]X, 9a, and ht-[(p-MeC(6)H(4))Pt(micro-PN)(micro-NP)PtMe(p-MeC(6)H(4))]X, 11, were further characterized by single crystal X-ray crystallography.     

Platinum(II) complexes bearing 1,1'-bis(diphenylphosphino)ferrocene as building blocks for functionalized redox active porphyrins

Reactions of the cationic complex ions [PtMe(Me2SO)(PP)]+ (PP = dppf (1,1'-bis(diphenylphosphino)ferrocene) and dppe (1,2-bis(diphenylphosphino)ethane)) with 5,10,15,20-tetrakis(4-pyridyl)-21H,23H-porphyrin (TpyP) led to the formation of the symmetrical tetraplatinated porphyrin complexes, [PtMe(PP)]4TpyP.X4 (PP = dppf, X = CF3SO3-, 3, and PP = dppe, X = BF4-, 5) containing the organometallic fragment [PtMe(PP)]. The precursor sulfoxide platinum complexes [PtMe(Me2SO)(dppf)]CF3SO3, 2 and [PtMe(Me2SO)(dppe)]BF4, 4, were prepared by halide abstraction from [PtMeCl(dppf)], 1, and by controlled protonolysis of [PtMe2(dppe)] respectively, in the presence of a small amount of dimethyl sulfoxide. All these starting platinum(II) compounds, as well as the porphyrin derivatives 3 and 5, were fully characterized through elemental analysis, 1H NMR mono- and bidimensional, 31P[1H], 31P-1H HMBC, UV/Vis absorption and photophysical measurements. The X-ray crystal structure of complex 1 has been determined. In order to ascertain the electronic influence of ferrocene, the spectroscopic and redox properties of 3 were compared with those of TPyP and of the analogous 5. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), 1H and 31P NMR data, and UV/Vis data, all suggest a certain degree of communication between the central porphyrin and the peripheral hetero-bimetallic fragments. In contrast, no detectable interaction among these peripheral groups seem to come into play. Unlikely from the porphyrin derivative 5, formation of well defined fluorescent mesoscopic ring structures was easily achieved by simple evaporation from diluted dichloromethane solutions of 3.     

Carbon‐iodide bond activation by cyclometalated Pt (II) complexes bearing tricyclohexylphosphine ligand: A comparative kinetic study and theoretical elucidation

Cyclometalated Pt (II) complexes [PtMe(C^N)(L)], in which C^N = deprotonated 2,2′‐bipyridine N‐oxide (Obpy), 1 , deprotonated 2‐phenylpyridine (ppy), 2 , deprotonated benzo [h] quinolone (bzq), 3 , and L = tricyclohexylphosphine (PCy₃) were prepared and fully characterized. By treatment of 1–3 with excess MeI, the thermodynamically favored Pt (IV) complexes cis‐[PtMe₂I(C^N)(PCy₃)] (C^N = Obpy, 1a ; ppy, 2a ; and bzq, 3a ) were obtained as the major products in which the incoming methyl and iodine groups adopted cis positions relative to each other. All the complexes were characterized by means of NMR spectroscopy while the absolute configuration of 1a was further determined by X‐ray crystal structure analysis. The reaction of methyl iodide with 1–3 were kinetically explored using UV–vis spectroscopy. On the basis of the kinetic data together with the time‐resolved NMR investigation, it was established that the oxidative addition reaction occurred through the classical S_N2 attack of Pt (II) center on the MeI reagent. Moreover, comparative kinetic studies demonstrated that the electronic and steric nature of either the cyclometalating ligands or the phosphine ligand influence the rate of reaction. Surprisingly, by extending the oxidative addition reaction time, very stable iodine‐bridged Pt (IV)‐Pt (IV) complexes [Pt₂Me₄(C^N)₂(μ‐I)₂] (C^N = Obpy, 1b ; ppy, 2b ; and bzq, 3b ) were obtained and isolated. In order to find a reasonable explanation for the observation, a DFT (density functional theory) computational analysis was undertaken and it was found that the results were consistent with the experimental findings.     

Mechanisms of C-C and C-H alkane reductive eliminations from octahedral Pt(IV): reaction via five-coordinate intermediates or direct elimination?

The Pt(IV) complexes P(2)PtMe(3)R [P(2) = dppe (PPh(2)(CH(2))(2)PPh(2)), dppbz (o-PPh(2)(C(6)H(4))PPh(2)); R = Me, H] undergo reductive elimination reactions to form carbon-carbon or carbon-hydrogen bonds. Mechanistic studies have been carried out for both C-C and C-H coupling reactions and the reductive elimination reactions to form ethane and methane are directly compared. For C-C reductive elimination, the evidence supports a mechanism of initial phosphine chelate opening followed by C-C coupling from the resulting five-coordinate intermediate. In contrast, mechanistic studies on C-H reductive elimination support an unusual pathway at Pt(IV) of direct coupling without preliminary ligand loss. The complexes fac- P(2)PtMe(3)R (P(2) = dppe, R = Me, H; P(2) = dppbz, R = Me) have been characterized crystallographically. The Pt(IV) hydrides, fac-P(2)PtMe(3)H (P(2) = dppe, dppbz), are rare examples of stable phosphine ligated Pt(IV) alkyl hydride complexes.     

A series of dinuclear homo- and heterometallic complexes with two or three bridging sulfido ligands derived from the tungsten tris(sulfido) complex [Et(4)N][(Me(2)Tp)WS(3)] (Me(2)Tp = hydridotris(3,5-dimethylpyrazol-1-yl)borate)

The generation of heterobimetallic complexes with two or three bridging sulfido ligands from mononuclear tris(sulfido) complex of tungsten [Et(4)N][(Me(2)Tp)WS(3)] (1; Me(2)Tp = hydridotris(3,5-dimethylpyrazol-1-yl)borate) and organometallic precursors is reported. Treatment of 1 with stoichiometric amounts of metal complexes such as [M(PPh(3))(4)] (M = Pt, Pd), [(PtMe(3))(4)(micro(3)-I)(4)], [M(cod)(PPh(3))(2)][PF(6)] (M = Ir, Rh; cod = 1,5-cyclooctadiene), [Rh(cod)(dppe)][PF(6)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)), [CpIr(MeCN)(3)][PF(6)](2) (Cp = eta(5)-C(5)Me(5)), [CpRu(MeCN)(3)][PF(6)], and [M(CO)(3)(MeCN)(3)] (M = Mo, W) in MeCN or MeCN-THF at room temperature afforded either the doubly bridged complexes [Et(4)N][(Me(2)Tp)W(=S)(micro-S)(2)M(PPh(3))] (M = Pt (3), Pd (4)), [(Me(2)Tp)W(=S)(micro-S)(2)M(cod)] (M = Ir, Rh (7)), [(Me(2)Tp)W(=S)(micro-S)(2)Rh(dppe)], [(Me(2)Tp)W(=S)(micro-S)(2)RuCp] (10), and [Et(4)N][(Me(2)Tp)W(=S)(micro-S)(2)W(CO)(3)] (12) or the triply bridged complexes including [(Me(2)Tp)W(micro-S)(3)PtMe(3)] (5), [(Me(2)Tp)W(micro-S)(3)IrCp][PF(6)] (9), and [Et(4)N][(Me(2)Tp)W(micro-S)(3)Mo(CO)(3)] (11), depending on the nature of the incorporated metal fragment. The X-ray analyses have been undertaken to clarify the detailed structures of 3-5, 7, and 9-12.     

Synthesis,characterization and optical properties of a new cationic cyclometalated platinum(ii) complex

The cyclometalated platinum (II) complex, [Pt(ppy)(ppyH)₂] OTF, 2 , in which ppy and ppyH denote the cyclometalated and non‐cyclometalated 2‐phenylpyridine ligand respectively, was prepared from the reaction of the platinum(IV) complex [PtMe₃(OTF)], 1 , with 3 equiv 2‐phenylpyridine at room temperature. The cyclometalated complex 2 was characterized using ¹H NMR spectroscopy. The solid state structure of 2 was further identified by single crystal X‐ray structure determination. 2 displays a green emission in solution and in solid state at room temperature and TD‐DFT calculations is used to elucidate the origin of the electronic transitions in the UV–vis spectrum of 2 .     

Organoplatinum(II) complexes containing chelating or bridging bis(N-heterocyclic carbene) ligands: formation of a platinum(II) carbonate complex by aerial CO2 fixation

The preparation of two new bis(N-heterocyclic carbene) platinum(II) complexes, in which NHC rings are joined by a CH(2) linker group, is described. While, the chelate complex [PtMe(2)(bis-NHC1)], 1, was formed with large tert-butyl wingtips, the iso-propyl N-substituent analogue favors formation of the cluster complex [Pt(2)Me(4)(μ-SMe(2))(μ-bis-NHC2)](2)(μ-Ag(2)Br(2)), 2, in which two binuclear platinum(II) complexes are linked together by an Ag(2)Br(2) unit. The chelating platinum complex 1 undergoes aerial CO(2) fixation and forms platinum(II) carbonate complex [Pt(CO(3))(bis-NHC1)], 3.     

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.     

Organoplatinum(IV) tris-chelate complexes, each having a cyclic metallacarbonate ring: synthesis, characterization and kinetic studies of the formation

The complexes [Pt[(CH2)4](NN)], 1a (NN = 2,2'-bipyridine) and 1b (NN = 1,10-phenanthroline) react with 2,3-epoxypropylphenyl ether in the presence of CO2 to give tris-chelate platina(IV)cyclopentane complexes characterized by 1H and 13C NMR spectroscopy as [Pt[(CH2)4](CH2CHCH2OPhOCO2)(NN)], 2. The reactions proceed by the SN2 mechanism and the rates were independent of concentration of CO2. It is demonstrated that for 1a, the reaction proceeds 2.32 times faster than the similar reaction in which the dimethyl analog, [PtMe2(2,2'-bipyridine)], is used. The analog tris-chelate complex [Pt[(CH2)4](CH2CHPhOCO2)(phen)], 3a, was similarly synthesized.     

PtMe(iPr3P)2]+: a Pt(II) complex with an agostic interaction that undergoes C-H activation

The T-shaped Pt(II) complex [PtMe(iPr3P)2][1-H-closo-CB11Me11], which is stabilised by an agostic interaction, undergoes acid-catalysed intramolecular C-H activation in the presence of THF to afford cyclometallated [Pt(THF)(iPr3P)(iPr2PCHMeCH2)][1-H-closo-CB11Me11].     

Oxidative addition of Ph2TeCl2 to a dimethylplatinum(II) complex: effects of secondary bonding in the platinum-tellurium products

In the first example of oxidative addition of tellurium-halide bonds to a transition-metal complex, Ph(2)TeCl(2) reacts with [PtMe(2)(bu(2)bpy)], 1, bu(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine, to give an organoplatinum(IV) complex that can be formulated as an ionic diphenyl telluride complex [PtClMe(2)(TePh(2))(bu(2)bpy)]Cl or as a neutral chlorodiphenyltelluryl complex [PtClMe(2)(TePh(2)Cl)(bu(2)bpy)]; the complex contains an unusually long Te...Cl bond length of 3.43 A. The weakly bound chloride ligand is easily removed by reaction with AgO(3)SCF(3) to give the cationic complex [PtClMe(2)(TePh(2))(bu(2)bpy)](CF(3)SO(3)) in which the triflate anion is not coordinated to tellurium. This complex reacts with a second 1 equiv of AgO(3)SCF(3) to give the aqua complex [PtMe(2)(OH(2))(TePh(2)..O(3)SCF(3))(bu(2)bpy)](CF(3)SO(3)), in which a triflate anion forms secondary bonds with both the aqua and TePh(2) ligands. In these platinum(IV) complexes, the magnitude of the coupling constant (1)J(PtTe) is strongly influenced by the presence of the weakly bonded Te...X groups.     

Oxidative addition of MeI to some cyclometalated organoplatinum(II) complexes: Kinetics and mechanism

New cyclometalated platinum(II) complexes [PtMe(C^N)L], 1, in which C^N = deprotonated 2-phenylpyridine (ppy), benzo[h]quinoline (bhq) or 2-(p-tolyl)pyridine (tpy) and L = PPh₃ or PMePh₂, were synthesized by the reaction of [PtMe(C^N)(SMe₂)] with 1 equiv of L. The reaction of complexes 1 with MeI gave the cyclometalated Pt(IV) complexes [PtMe₂I(C^N)L], 3. On the basis of kinetic studies, using Uv–visible spectroscopy, it was suggested that the latter oxidative addition reactions were proceeded by an S_N2 mechanism. The rates of the reactions at different temperatures were measured and consistent with the proposed mechanism, large negative ΔS³ values were found for each reaction. Besides, rate of reactions (in CHCl₃) involving the PPh₃ complexes [PtMe(C^N)(PPh₃)], were almost 3–5 times slower than those involving the PMePh₂ complexes [PtMe(C^N)(PMePh₂)]. This was attributed to the electronic and steric effects of PPh₃ ligand as compared with that of PMePh₂ ligand which was further confirmed using density functional theory (DFT) calculations through finding approximate structures for the described complexes.     

Reactivity of TCNE or TCNQ derivatives of quinonoid zwitterions: platinum-induced HCN elimination vs oxidative-addition

The reaction of the functional, zwitterionic quinonoid molecule (6E)-4-(butylamino)-6-(butyliminio)-3-oxo-2-(1,1,2,2-tetracyanoethyl)cyclohexa-1,4-dien-1-olate, [C(6)H-2-{C(CN)(2)C(CN)(2)H}]-4,6-(···NH n-Bu)(2)-1,3(···O)(2) (2), which has been previously prepared by regioselective insertion of TCNE into the C-H bond adjacent to the C···O bonds of the zwitterionic benzoquinone monoimine (6E)-4-(butylamino)-6-(butyliminio)-3-oxocyclohexa-1,4-dien-1-olate, C(6)H(2)-4,6-(···NHn-Bu)(2)-1,3-(···O)(2) (1), with 2 equiv of [Pt(C(2)H(4))(PPh(3))(2)], afforded the Pt(0) complex [Pt(PPh(3))(2)(4)] (6) (4 = 2-HCN; (6E)-4-(butylamino)-6-(butyliminio)-3-oxo-2-(1,2,2-tricyanoethenyl)cyclohexa-1,4-dien-1-olate), in which a tricyanoethenyl moiety is π-bonded to the metal. A metal-induced HCN elimination reaction has thus taken place. The same complex was obtained directly by the reaction of 1 equiv of the Pt(0) complex [Pt(C(2)H(4))(PPh(3))(2)] with the olefinic ligand [C(6)H-2-{C(CN)═C(CN)(2)}]-4,6-(···NHn-Bu)(2)-1,3-(···O)(2)) (4), previously obtained by the reaction of 2 with NEt(3) in THF. A similar reactivity pattern was observed between 2 and 2 equiv of the Pd(0) precursor [Pd(dba)(2)] in the presence of dppe, which led to [Pd(dppe)(4)] (7), which was also directly obtained from 4 and 1 equiv [Pd(dba)(2)]/dppe. In contrast to the behavior of the TCNE derivative 2, the reaction of the TCNQ derivative (6E)-4-(butylamino)-6-(butyliminio)-2-(dicyano(4-(dicyanomethyl)phenyl)methyl)-3-oxocyclohexa-1,4-dien-1-olate, [C(6)H-2-{C(CN)(2)p-C(6)H(4)C(CN)(2)H}]-4,6-(···NHn-Bu)(2)-1,3-(···O)(2)) (3), with 2 equiv of [Pt(C(2)H(4))(PPh(3))(2)] led to formal oxidative-addition of the C-H bond of the C(CN)(2)H moiety to give the Pt(II) hydride complex trans-[PtH(PPh(3))(2){N═C═C(CN)p-C(6)H(4)C(CN)(2)-2-[C(6)H-4,6-(···NHn-Bu)(2)-1,3-(···O)(2))}] (8). The molecular structures of 3, 4, 6·0.5(H(2)O), and 8·3(CH(2)Cl(2)) have been determined by single-crystal X-ray diffraction.     

Unsymmetrical platinum(II) phosphido derivatives: oxidation and reductive coupling processes involving platinum(III) complexes as intermediates

Reaction of the trinuclear [NBu 4] 2[(R F) 2Pt(mu-PPh 2) 2Pt(mu-PPh 2) 2Pt(R F) 2] ( 1, R F = C 6F 5) with HCl results in the formation of the unusual anionic hexanuclear derivative [NBu 4] 2[{(R F) 2Pt(mu-PPh 2) 2Pt(mu-PPh 2) 2Pt(mu-Cl)} 2] ( 4, 96 e (-) skeleton) through the cleavage of two Pt-C 6F 5 bonds. The reaction of 4 with Tl(acac) yields the trinuclear [NBu 4][(R F) 2Pt(mu-PPh 2) 2Pt(mu-PPh 2) 2Pt(acac)] ( 5, 48 e (-) skeleton), which is oxidized by Ag (+) to form the trinuclear compound [(R F) 2Pt(mu-PPh 2) 2Pt(mu-PPh 2) 2Pt(acac)][ClO 4] ( 6, 46 e (-) skeleton) in mixed oxidation state Pt(III)-Pt(III)-Pt(II), which displays a Pt-Pt bond. The reduction of 6 by [NBu 4][BH 4] gives back 5. The treatment of 6 with Br (-) (1:1 molar ratio) at room temperature gives a mixture of the isomers [(PPh 2R F)(R F)Pt(mu-PPh 2)(mu-Br)Pt(mu-PPh 2) 2Pt(acac)], having Br trans to R F ( 7a) or Br cis to R F ( 7b), which are the result of PPh 2/C 6F 5 reductive coupling. The treatment of 5 with I 2 (1:1 molar ratio) yields the hexanuclear [{(PPh 2R F)(R F)Pt(mu-PPh 2)(mu-I)Pt(mu-PPh 2) 2Pt(mu-I)} 2] ( 8, 96 e (-) skeleton), which is easily transformed into the trinuclear compound [(PPh 2R F)(R F)Pt(mu-PPh 2)(mu-I)Pt(mu-PPh 2) 2Pt(I)(PPh 3)] ( 9, 48 e (-) skeleton). Reaction of [(R F) 2Pt(mu-PPh 2) 2Pt(mu-PPh 2) 2Pt(NCMe) 2] ( 10) with I 2 at 213 K for short reaction times gives the trinuclear platinum derivative [(R F) 2Pt(mu-PPh 2) 2Pt(mu-PPh 2) 2Pt(I) 2] ( 11, 46e skeleton) in mixed oxidation state Pt(III)-Pt(III)-Pt(II) and with a Pt-Pt bond, while the reaction at room temperature and longer reactions times gives 8. The structures of the complexes have been established by multinuclear NMR spectroscopy. In particular, the (195)Pt NMR analysis, carried out also by (19)F- (195)Pt heteronuclear multiple-quantum coherence, revealed an unprecedented shielding of the (195)Pt nuclei upon passing from Pt(II) to Pt(III). The X-ray diffraction structures of complexes 4, 5, 6, 9, and 11 have been studied. A detailed study of the relationship between the complexes has been carried out.