Synthesis of the pivalamidate-bridged pentanuclear platinum(II,III) linear complexes with Pt...Pt interactions

Pentanuclear linear chain Pt(II,III) complexes [[Pt2(NH3)2X2((CH3)3CCONH)2(CH2COCH3)]2[PtX'4]].nCH3COCH3 (X = X' = Cl, n = 2 (1a), X = Cl, X' = Br, n = 1 (1b), X = Br, X' = Cl, n = 2 (1c), X = X' = Br, n = 1 (1d)) composed of a monomeric Pt(II) complex sandwiched by two amidate-bridged Pt dimers were synthesized from the reaction of the acetonyl dinuclear Pt(III) complexes having equatorial halide ligands [Pt2(NH3)2X2((CH3)3CCONH)2(CH2COCH3)]X' ' (X = Cl (2a), Br (2b), X' ' = NO3-, CH3C6H4SO3-, BF4-, PF6-, ClO4-), with K2[PtX'4] (X' = Cl, Br). The X-ray structures of 1a-1d show that the complexes have metal-metal bonded linear Pt5 structures, and the oxidation state of the metals is approximately Pt(III)-Pt(III)...Pt(II)...Pt(III)-Pt(III). The Pt...Pt interactions between the dimer units and the monomer are due to the induced Pt(II)-Pt(IV) polarization of the Pt(III) dimeric unit caused by the electron withdrawal of the equatorial halide ligands. The density functional theory calculation clearly shows that the Pt...Pt interactions between the dimers and the monomer are made by the electron transfer from the monomer to the dimers. The pentanuclear complexes have flexible Pt backbones with the Pt chain adopting either arch or sigmoid structures depending on the crystal packing.     

Structural basis for vapoluminescent organoplatinum materials derived from noncovalent interactions as recognition components

The spectroscopic properties and crystal structures of a series of platinum(II) complexes bearing functionalized sigma-alkynyl groups, namely [(tBu(2)bpy)Pt(C triple bond CAr)(2)] (tBu(2)bpy = 4,4'-bis-tert-butyl-2,2'-bipyridine, Ar = 4-pyridyl, 1; 3-pyridyl, 2; 2-pyridyl, 3; 4-ethynylpyridyl, 4; 2-thienyl, 5; pentafluorophenyl, 6) have been studied. Solid-state emissions of 1 and 6 are dependent on their crystallinity. Reversible and selective vapoluminescence was observed for 1 and 6 in the presence of chlorocarbon vapors. For solid 1, dramatic enhancement of green luminescence is observed upon sorption of CH(2)Cl(2) or CHCl(3) vapor. The excimeric orange emission for solid 6 is switched to monomeric green emission upon exposure to CH(2)Cl(2) vapor. The luminescent responses of a thin film of 1 towards various organic vapors have also been examined. In the crystallographically determined structure of 1.CH(2)Cl(2), the bis(acetylide) moiety acts as the receptor berth for a CH(2)Cl(2) molecule through concerted C-H.pi(C triple bond C) interactions, while Cl.Cl interactions connect the CH(2)Cl(2) molecules into infinite linear chains. The observed crystal lattices are arranged into scaffolds of varying porosity by weak C-H...N(py) (1.CH(2)Cl(2), 1.CH(3)CN, 4.DMF) and C-H...F-C (6, 6.CH(3)CN) interactions. The correlation between the crystal structures of 1.CH(2)Cl(2), 1.CH(3)CN, 2, 4.DMF, 5, 6, and 6.CH(3)CN and their vapoluminescence suggests that weak nonconventional hydrogen-bonding interactions preside over the reversible sensing and signalling processes.     

Influence of solvent and weak C-H...O contacts in the self-assembled [Pt2M4{CC(3-OMe)C6H4}8] (M = Cu, Ag) clusters and their role in the luminescence behavior

New alkynyl complexes [Pt2M4{CC(3-OMe)C6H4}8] (M = Ag 1, Cu 2) have been synthesized and their structures and properties compared to those of related [Pt2M4(CCPh)8] compounds. For the Pt-Ag derivatives, the X-ray structures of the discrete yellow solvate monomer, [Pt2Ag4{CC(3-OMe)C6H4}8].2THF ([1.2THF]), and the dark garnet unsolvated polymeric form, [Pt2Ag4{CC(3-OMe)C6H4}8](infinity) ([1](infinity)), are presented. The yellow form ([1.2THF]) exhibits a distorted octahedral geometry of the metal centers with the platinum atoms mutually trans and the four silver atoms in the equatorial plane. Pairs of Ag atoms are weakly bridged by THF molecules [mu-Ag2...O(THF)]. The garnet form ([1](infinity)) has an unprecedented infinite stacked chain of octahedral clusters linked by short Pt...Pt bonds (3.1458(8) A). In both forms, different types of weak C-H...O (OMe) hydrogen bonds are observed. For comparative purposes, we have also provided the crystal structures of the yellow monomer form, [Pt2Ag4-(CCPh)8].CHCl3, and the red dimer form, [Pt2Ag4(CCPh)8]2 (Pt-Pt 3.221(2) A). These clusters display intense photoluminescence in both solution and the solid state, at room temperature and 77 K. The emission observed for the yellow form [1.2THF] in the solid state is assigned to a 3MLM'CT [Pt(d)/pi(CCR) --> Pt(p(z))/Ag(sp)/pi(CCR)] state modified by Pt...Ag, Ag...Ag, and Ag...(THF) contacts. However, in the garnet form [1](infinity) and in 2, the emissions are related to the axial Pt-Pt bonds and are assigned as phosphorescence from a metal-metal-to-ligand charge-transfer (3MMLCT) excited state ([1](infinity)), or an admixture of a metal-metal (Pt-Pt) centered 3(dsigmap(z)sigma) and 3MMLCT excited state (2). For 1, a remarkable quenching and a shift to higher energies in the emission is observed on changing from CH2Cl2 to THF, and for both 1 and 2, the emission spectra at 77 K varies with the concentration, showing their tendency to stack even in glass.     

Platinum diimine bis(acetylide) complexes: synthesis, characterization, and luminescence properties

A new set of luminescent platinum(II) diimine complexes has been synthesized and characterized. The anionic ligands in these complexes are arylacetylides. The complexes are brightly emissive in fluid solution with relative emission quantum yields phiem ranging from 3 x 10(-3) to 10(-1). Two series of complexes have been investigated. The first has the formula Pt(Rphen)(C...CC6H5)2 where Rphen is 1,10-phenanthroline substituted in the 5-position with R = H, Me, Cl, Br, NO2, or C...CC6H5, while the second has the formula Pt(dbbpy)(C=CC6H4X)2 where dbbpy = 4,4'-di(tert-butyl)bipyridine and X = H, Me, F, or NO2. From NMR, IR, and electronic spectroscopies, all of the complexes are assigned a square planar coordination geometry with cis-alkynyl ligands. The crystal structure of Pt(phen)(Ce-CC6H4CH3)2 confirms this assignment. All of the complexes exhibit an absorption band at ca. 400 nm that corresponds to a Pt d-->pi*diimine charge-transfer transition. The variation of lambdamax for this band with substituent variation supports this assignment. From similar changes in the energy of the solution luminescence as a function of substituents R and X, the emissive excited state is also of MLCT origin, but with spin-forbidden character on the basis of excited-state lifetime measurements (0.01-5.6 micros). The complexes undergo electron-transfer quenching, showing good Stern-Volmer behavior using 10-methylphenothiazine and N,N,N',N'-tetramethylbenzidine as reductive quenchers. Excited-state reduction potentials are estimated on the basis of a simple thermochemical analysis. Crystal data for Pt(phen)(C...CC6H4CH3)2: monoclinic, space group C2/c, a = 19.0961(1) A, b = 10.4498(1) A, c = 11.8124(2) A, beta = 108.413(1) degrees, V = 2236.49 A3, number of reflections 1614, number of variables 150, R1 = 0.0163, wR2 (I > 2sigma) = 0.0410.     

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.     

Copolymerization of silyl vinyl ethers with olefins by (alpha-diimine)PdR+

This paper reports that (alpha-diimine)PdMe+ catalyzes the copolymerization of olefins and silyl vinyl ethers. The reactions of (alpha-diimine)PdMe+ (alpha-diimine = (2,6-iPr2-C6H3)N=CMe-CMe=N(2,6-iPr2-C6H3)) with excess vinyl ethers CH2=CHOR (1a-d: R = tBu (a), SiMe3 (b), SiPh3 (c), Ph (d)) in CH2Cl2 at 20 degrees C afford polymers for 1a (rapidly) and 1b (slowly) but not for 1c or 1d. The structures of poly(1a,b) indicate a cationic polymerization mechanism. The reaction of (alpha-diimine)PdMe+ with 1-2 equiv of 1a-d proceeds by sequential C=C pi-complexation to form (alpha-diimine)PdMe(CH2=CHOR)+ (2a-d), 1,2 insertion to form (alpha-diimine)Pd(CH2CHMeOR)+ (3a-d), reversible isomerization to (alpha-diimine)Pd(CMe2OR)+ (4a-d), beta-OR elimination to generate (alpha-diimine)Pd(OR)(CH2=CHMe)+ (not observed), and allylic C-H activation to yield (alpha-diimine)Pd(eta3-C3H5)+ (5) and ROH. The reaction of (alpha-diimine)PdMe+ with 1-hexene/1b and 1-hexene/1c mixtures in CH2Cl2 at 20 degrees C affords copolymers containing up to 20 mol % silyl vinyl ether. The copolymers were purified to be free of any -[CH2CHOSiR3]n- homopolymer. The copolymer structures are similar to that of homopoly(1-hexene) generated under the same conditions. The major comonomer units are CH3CH(OSiR3)CH2-, CH2(OSiR3)CH2- and -CH2CH(OSiR3)CH2-. The 1-hexene/CH2=CHOSiR3 copolymers can be desilylated to give 1-hexene/CH2=CHOH copolymers. The results of control experiments argue against cationic and radical mechanisms for the copolymerization, and an insertion/chain-walking mechanism is proposed.     

Synthesis and characterization of nickel(II) bis(alkylthio)salen complexes

NiX2(2-RSC6H4CH=NCH2CH2N=CHC6H4SR-2) (NiX2L; L = 5) (1a, X = Br, R = C6H13; 1b, X = Cl, R = C12H25) and NiX2(2-C6H13SC6H4CH2NHCH2CH2NHCH2C6H4SC6H13-2) (NiX2L; L = 6) (2a, X = Br; 2b, X = Cl; 2c, X = OClO3) were prepared from ligands 5 and 6, respectively. The 1:2 metal-ligand complex Ni(OClO3)2(2-RSC6H4CH2NHCH2CH2NHCH2C6H4SR-2)2 3, was obtained from an EtOH solution of 2c. The characterization of paramagnetic 1-3 included single-crystal X-ray diffraction studies of 1a and 3. Complex 2c converted into 3 in the presence of excess ligand 6 in CHCl3.     

Functionalized corannulene cations: a detailed theoretical survey

The first theoretical investigation of a series of surface-decorated corannulene cations, {R-C(20)H(10)}(+), where R = H, CH(3), CH(2)Cl, CHCl(2), and CCl(3), is accomplished. Three possible isomers of {R-C(20)H(10)}(+) such as hub-, rim-, and spoke-functionalized corannulene derivatives are considered and compared. The trends in their stability and transition barriers are provided. A detailed study of energetics of {R-C(20)H(10)}(+) is complemented by in-depth investigation of their electronic structures and aromaticity.     

Luminescent mu-ethynediyl and mu-butadiynediyl binuclear gold(I) complexes: observation of (3)(pi pi*) emissions from bridging C(n)(2-) units.

The synthesis and X-ray structural and spectroscopic characterization for LAuC triple bond CAuL x 4CHCl(3) and LAuC triple bond C--C triple bond CAuL x 2CH(2)Cl(2) (1 x 4CHCl(3) and 2 x 2CH(2)Cl(2), respectively; L = PCy(3), tricyclohexylphosphine) are reported. The bridging C(n)(2-) units are structurally characterized as acetylene or diacetylene units, with C triple bond C distances of 1.19(1) and 1.199(8) A for 1 x 4CHCl(3) and 2 x 2CH(2)Cl(2), respectively. An important consequence of bonding to Au(I) for the C(n)(2-) moieties is that the lowest-energy electronic excited states, which are essentially acetylenic (3)(pi pi*) in nature, acquire sufficient allowedness via Au spin-orbit coupling to appear prominently in both electronic absorption and emission spectra. The origin lines for both complexes are well-defined and are observed at 331 and 413 nm for 1 and 2, respectively. Sharp vibronic progressions corresponding to v(C triple bond C) are observed in both emission and absorption spectra. The acetylenic (3)(pi pi) excited state of 2 has a long lifetime (tau(0) = 10.8 mus) in dichloromethane at room temperature and is a powerful reductant (E degrees [Au(2)(+)/Au(2)] < or = -1.85 V vs SSCE).     

Diplatinum alkynyl chromophores as sensitisers for lanthanide luminescence in Pt2Ln2 and Pt2Ln4 (Ln = Eu, Nd, Yb) arrays with acetylide-functionalized bipyridine/phenanthroline

Incorporation of diplatinum complex Pt2(micro-dppm)2(bpyC[triple bond]C)4 or Pt2(mu-dppm)2(phenC[triple bond]C)4 with Ln(hfac)3(H2O)2 (Ln = Nd, Eu, Yb) gave a series of Pt2Ln2 and Pt2Ln4 bimetallic arrays, in which the excitation of d(Pt) -->pi*(R-C[triple bond]C) MLCT absorption induces sensitisation of lanthanide luminescence through efficient d --> f energy transfer from Pt(II) alkynyl chromophores.     

Importance of entropy in the diastereoselectivity of 5-substituted 2-methyladamant-2-yl cations

The diastereofacial selectivity of 2-methyl-5-X-adamant-2-yl cations IX (X = CN, Cl, Br, CH3O, COOCH3, C6H5, CH3, and (CH3)3Sn) toward methanol has been investigated in the gas phase at 750 Torr and in the 40-120 degrees C temperature range and compared with that of IF (X = F) and ISi (X = (CH3)3Si) measured previously under similar conditions. Detailed analysis of the energy surface of the IMe (X = CH3) ion reveals that the activation barrier of its syn addition to methanol is significantly lower than that of the anti attack. In the 40-100 degrees C range, such a difference is strongly reduced by adverse entropic factors which are large enough to invert the IMe diastereoselectivity from syn to anti at T > 69 degrees C. The behavior of IMe diverges markedly from that of IF and ISi. Large adverse entropic factors account for the predominant syn diastereoselectivity observed in the reaction with IF (X = F), notwithstanding the anti enthalpy barrier is lower than the syn one. Adverse entropy plays a minor role in the reaction with ISi (X = (CH3)3Si) which instead exhibits a preferred anti diastereoselectivity governed by the activation enthalpies. Depending on the electronic properties of X, the kinetic behavior of the other IX ions obeys one of the above models. The gas-phase diastereoselectivity of IX ions responds to a subtle interplay between the sigma-hyperconjugative/electrostatic effects of the X substituent and the activation entropy terms. sigma-Hyperconjugation/field effects determine the pyramidal structure and the relative stability of the syn and anti conformers of IX as well as the relative stability of their addition transition structures and their position along the reaction coordinate. The diastereoselectivity of IX in the gas phase is compared with that measured in solution and with theoretical predictions.     

Coordination studies of a new unsymmetrical kappa4-PNN'N"-tetradentate ligand: stepwise formation and structural characterization

The two-step synthesis of a new unsymmetrical ligand 2-[Ph2PC6H4C(H)=N]C6H4[N(H)COCH2N(H)CO2Bz], 2.HH, via acid-catalyzed Schiff base condensation of 2-(H2N)C6H4[N(H)COCH2N(H)CO2Bz], 1, with 2-Ph2PC6H4(CHO) in refluxing EtOH is reported. The multidentate ligand 2.HH, isolated in ca. 60% yield, exhibits an array of ligation modes, as exemplified by coordination studies with NiII, PdII, PtII, and AuI mononuclear metal precursors. Hence, reaction of 2.HH with AuCl(tht) (1:1 molar ratio, tht = tetrahydrothiophene) affords AuCl(2.HH), 3, in which the ligand behaves as a classic, neutral two-electron phosphorus donor. In contrast, reaction with MCl2(cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) affords the corresponding dichloro complexes MCl2(2.HH) (4a M = Pt; 4b M = Pd) in which kappa2-P/N-chelation through both P and imino N-donor atoms is observed. Likewise, treatment of Pd(CH3)Cl(cod) with 2.HH gave Pd(CH3)Cl(2.HH), 4c, in which the imino nitrogen is trans to the methyl ligand. Cycloocta-1,5-diene elimination from, and single methyl protonation of, Pt(CH3)2(cod) with 1 equiv of 2.HH in toluene at ambient temperature affords the neutral complex Pt(CH3)(2.H-), 5a, in which 2.H- functions effectively in a kappa3-PNN' coordination mode. The dichloro compounds 4a or 4b undergo smooth N(H) deprotonation with tBuOK to give 6a\6a' and 6b\6b' in which 22- acts as a dianionic kappa4-PNN'N' ' ligand. The corresponding square-planar, diamagnetic, nickel(II) complex 6c\6c' was prepared in excellent yield from NiCl2.6H2O, 2.HH, and tBuOK. Variable-temperature NMR experiments confirm 6a\6a' and 6b\6b' exist, in solution, as a pair of conformational (anti and syn) isomers due to restricted rotation about the N-CO2Bz group. This feature is also borne out by single-crystal X-ray studies of anti-6a.CHCl3, syn-6a'.H2O, anti-6b.CHCl3, and anti-6c.CH2Cl2. To the best of our knowledge, we believe these constitute the first examples of crystallographically characterized conformers of a tetradentate ligand incorporating a P-donor center. All new compounds reported have been fully characterized by a combination of spectroscopic (NMR, FT-IR, ES-MS) and analytical methods. Furthermore, single-crystal X-ray studies have also been undertaken on compounds 2.HH, 3, 4a, and 5a.Et2O.     

Experimental and theoretical studies on the nature of weak nonbonded interactions between divalent selenium and halogen atoms

To investigate the nature of weak nonbonded selenium...halogen interactions (Se...X interactions; X = F, Cl, and Br), three types of model compounds [2-(CH(2)X)C(6)H(4)SeY (1-3), 3-(CH(2)X)-2-C(10)H(6)SeY (4-6), and 2-XC(6)H(4)CH(2)SeY (7-9); Y = CN, Cl, Br, SeAr, and Me] were synthesized, and their (77)Se NMR spectroscopic behaviors were analyzed in CDCl(3). The gradual upfield shifts of (77)Se NMR absorptions observed for series 1-3 and 4-6 suggested that the strength of Se...X interaction decreases in the order of Se...F > Se...Cl > Se...Br. The quantum chemical calculations at the B3LYP/631H level using the polarizable continuum model (PCM) revealed that the most stable conformer for 1-3 is the one with an intramolecular short Se...X atomic contact in CHCl(3) (epsilon = 4.9) and also that the n(X) --> sigma(Se-Y) orbital interaction (E(Se...X)) can reasonably explain the order of strength for the Se...X interactions. On the other hand, the (77)Se NMR absorptions observed for series 7-9 did not shift significantly from the reference compounds (C(6)H(5)CH(2)SeY), indicating the absence of the Se...X interaction for 7-9 presumably due to attenuation of basicity for the halogen atom that is substituted directly to the aromatic ring. These observations suggested that the n(X) --> sigma(Se-Y) orbital interaction is a dominant factor for formation of weak Se...X interactions. Electron correlation was also suggested to be important for the stability.     

On the unusual 2J(C2-H(f)) coupling dependence on syn/anti CHO conformation in 5-X-furan-2-carboxaldehydes

A remarkable difference for (2)J(C(2)-H(f)) coupling constant in syn and anti conformers of 5-X-furan-2-carboxaldehydes (X = CH(3), Ph, NO(2), Br) and a rationalization of this difference are reported. On the basis of the current knowledge of the Fermi-contact term transmission, a rather unusual dual-coupling pathway in the syn conformer is presented. The additional coupling pathway resembles somewhat that of the J(H-H) in homoallylic couplings, which are transmitted by hyperconjugative interactions involving the pi(C=C) electronic system. The homoallylic coupling pathway can be labeled as sigma*(C-H) <-- pi(C=C) --> sigma*(C-H). In the present case, this additional coupling pathway, using an analogous notation, can be labeled as sigma*(C(2)-C(C)) <-- LP(1)(O(1))...LP(2)(O(C)) --> sigma*(C(C)-H(f)) (sigma*(C(2)-C(C))) where O(1) and O(C) stand for the ring and carbonyl O atoms, respectively. This additional coupling pathway is not activated in the anti conformers since both oxygen lone pairs do not overlap.     

sp carbon chains surrounded by sp(3) carbon double helices: directed syntheses of wirelike Pt(CC)(n)Pt moieties that are spanned by two P(CH(2))(m)P linkages via alkene metathesis

Reactions of trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2PtCl (1; m' = a, 6; b, 7; c, 8; d, 9; e, 10) and H(CC)2H (HNEt2, cat. CuI) give trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)2H (3a-e, 80-95%). Oxidative homocouplings of 3a-d under Hay conditions (O2, cat. CuCl/TMEDA, acetone) yield trans,trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)4Pt(Ph2P(CH2)m'CH=CH2)2(C6F5) (4a-d, 64-84%). Treatment of 3c-e with excess HCCSiEt3 under Hay conditions gives trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)3SiEt3 (56-73%). Homocouplings (n-Bu4N+ F-, Me3SiCl, Hay conditions) afford trans,trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)6Pt(Ph2P(CH2)m'CH=CH2)2(C6F5) (13c-e, 59-64%). Reactions of 4a-d and 13c-e with Grubbs' catalyst, followed by hydrogenation, give mixtures of trans,trans-(C6F5)(Ph2P(CH2)mPPh2)Pt(CC)nPt(Ph2P(CH2)mPPh2)(C6F5) with termini-spanning diphosphines and trans,trans-(C6F5)(Ph2P(CH2)mPPh2)Pt(CC)nPt(Ph2P(CH2)mPPh2)(C6F5) with trans-spanning diphosphines (m = 2m' + 2; n = 4, 6). The latter (n = 4) are independently synthesized by similar metatheses/hydrogenations of 1a-d to give trans-(C6F5)(Ph2P(CH2)mPPh2)PtCl (49-59%), followed by analogous introductions of (CC)4 chains (66-77%). Crystal structures of complexes with termini-spanning diphosphines show sp3 chains with both double-helical (m/n = 20/4) and nonhelical (m/n = 20/6) conformations, and highly shielded sp chains. The sp3 chains of complexes with trans-spanning diphosphines exhibit double half-clamshell conformations. The dynamic properties of both classes of molecules are analyzed in detail.     

Magnitude and directionality of the interaction energy of the aliphatic CH/pi interaction: significant difference from hydrogen bond

The CCSD(T) level interaction energies of CH/pi complexes at the basis set limit were estimated. The estimated interaction energies of the benzene complexes with CH(4), CH(3)CH(3), CH(2)CH(2), CHCH, CH(3)NH(2), CH(3)OH, CH(3)OCH(3), CH(3)F, CH(3)Cl, CH(3)ClNH(2), CH(3)ClOH, CH(2)Cl(2), CH(2)FCl, CH(2)F(2), CHCl(3), and CH(3)F(3) are -1.45, -1.82, -2.06, -2.83, -1.94, -1.98, -2.06, -2.31, -2.99, -3.57, -3.71, -4.54, -3.88, -3.22, -5.64, and -4.18 kcal/mol, respectively. Dispersion is the major source of attraction, even if substituents are attached to the carbon atom of the C-H bond. The dispersion interaction between benzene and chlorine atoms, which is not the CH/pi interaction, is the cause of the very large interaction energy of the CHCl(3) complex. Activated CH/pi interaction (acetylene and substituted methanes with two or three electron-withdrawing groups) is not very weak. The nature of the activated CH/pi interaction may be similar to the hydrogen bond. On the other hand, the nature of other typical (nonactivated) CH/pi interactions is completely different from that of the hydrogen bond. The typical CH/pi interaction is significantly weaker than the hydrogen bond. Dispersion interaction is mainly responsible for the attraction in the CH/pi interaction, whereas electrostatic interaction is the major source of attraction in the hydrogen bond. The orientation dependence of the interaction energy of the typical CH/pi interaction energy is very small, whereas the hydrogen bond has strong directionality. The weak directionality suggests that the hydrogen atom of the interacting C-H bond is not essential for the attraction and that the typical CH/pi interaction does not play critical roles in determining the molecular orientation in molecular assemblies.     

Syntheses and Structures of the Complexes cis-[M(C(6)F(5))(2)(N&arcraise;X)] (M = Pd, Pt; N&arcraise;X = 2-Iodoaniline, 2-Benzoylpyridine) Containing N&arcraise;X Acting as a Didentate Chelating Ligand and Displaying I-->M or O-->M Interactions

Complexes cis-[M(C(6)F(5))(2)(THF)(2)] (M = Pd, Pt) are weak Lewis acids and react with the halocarbon ligand 2-iodoaniline (R-I) yielding the corresponding cis-[M(C(6)F(5))(2)(R-I)] [M = Pd (1), Pt (2)]. In these complexes a (C-)I-M bond is present. The use of other 2-haloanilines (halogen = F, Cl, Br) does not yield the analogous complexes because of the lesser nucleophilic character of the halogen involved. The presence of the (C-)I-Pt bond in 2 has been confirmed by an X-ray structure determination, which also reveals an N-H.M hydrogen bond between two neutral molecules. Complex 2 crystallizes in the space group P&onemacr;: Z = 4; a = 11.797(4) ?; b = 13.735(4) ?; c = 14.107(4) ?; alpha = 97.24(2) degrees; beta = 90.91(2) degrees; gamma = 99.44(2) degrees; V = 2235(2) ?(3). Similarly, complexes cis-[M(C(6)X(5))(2)(THF)(2)] (M = Pd, Pt; X = F, Cl) react with the ligand 2-benzoylpyridine {R-C(O)Ph}, in which the oxygen atom of the ketonic group can behave as a nucleophilic center, yielding the complexes cis-[M(C(6)X(5))(2){R-C(O)Ph}] [M = Pd, X = F (3); M = Pt, X = F (4), Cl (5)]. Complex 3 crystallizes in the space group C2/c: Z = 16; a = 26.284(3) ?; b = 10.623(1) ?; c = 31.423(4) ?; beta = 93.15(1) degrees; V = 8760(2) ?(3). The I-M or O-M bonds in complexes 1-5 are weak and can be easily broken by the addition of neutral (CO, PPh(3), and CH(3)CN) or anionic (Br(-)) ligands.     

Titanium and zirconium complexes of preorganized tripodal triaryloxide ligands

Tri(2-oxy-3,5-di-tert-butylphenyl)methane, [O3]3- has been used to prepare titanium and zirconium complexes of the general formula [O3]MX (M = Ti, X = NEt2, Cl, CH2Ph; M = Zr, X = CH2Ph). The tripodal [O3] ligand in titanium complexes adopt the syn- and the anti-conformation, while the syn complex of zirconium undergoes facile C-H activation to give a 5-carbametalatrane [O3C]Zr(THF)3.     

M2(hpp)4Cl2 and M2(hpp)4, where M = Mo and W: preparations, structure and bonding, and comparisons with C2, C2H2, and C2Cl2 and the hypothetical molecules M2(hpp)4(H)2

The reaction between M(2)Cl(2)(NMe(2))(4), where M = Mo or W, and Hhpp (8 equiv) in a solid-state melt reaction at 150 degrees C yields the compounds M(2)(hpp)(4)Cl(2) 1a (M = Mo) and 1b (M = W), respectively, by the elimination of HNMe(2) [hpp is the anion derived from deprotonation of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, Hhpp]. Purification of 1a and 1b is achieved by sublimation of the excess Hhpp and subsequent recrystallization from either CH(2)Cl(2) or CHCl(3) (or CDCl(3)). By single-crystal X-ray crystallography, the structures of 1a and 1b are shown to contain a central paddlewheel-like M(2)(hpp)(4) core with Mo-Mo = 2.1708(8) A (from CH(2)Cl(2)), 2.1574(5) A (from CDCl(3)), W-W = 2.2328(2) A (from CDCl(3)), and M-N = 2.09(1) (av) A. The Cl ligands are axially ligated (linear Cl-M-M-Cl) with abnormally long M-Cl bond distances that, in turn, depend on the presence or absence of hydrogen bonding to chloroform. The quadruply bonded compounds M(2)(hpp)(4), 2a (M = Mo), and 2b (M = W), can be prepared from the reactions between 1,2-M(2)R(2)(NMe(2))(4) compounds, where R = (i)()Bu or p-tolyl, and Hhpp (4 equiv) in benzene by ligand replacement and reductive elimination. The compounds 2a and 2b are readily oxidized, and in chloroform they react to form 1a and 1b, respectively. The electronic structure and bonding in the compounds 1a, 1b, 2a, and 2b have been investigated using gradient corrected density functional theory employing Gaussian 98. The bonding in the M-M quadruply bonded compounds, 2a and 2b, reveals M-M delta(2) HOMOs and extensive mixing of M-M pi and nitrogen ligand lone-pair orbitals in a manner qualitatively similar to that of the M(2)(formamidinates)(4). The calculations indicate that in the chloride compounds, 1a and 1b, the HOMO is strongly M-Cl sigma antibonding and weakly M-M sigma bonding in character. Formally there is a M-M triple bond of configuration pi(4)sigma(2), and the LUMO is the M-M delta orbital. An interesting mixing of M-M and M-Cl pi interactions occurs, and an enlightening analogy emerges between these d(4)-d(4) and d(3)-d(3) dinuclear compounds and the bonding in C(2), C(2)H(2), and C(2)Cl(2), which is interrogated herein by simple theoretical calculations together with the potential bonding in axially ligated compounds where strongly covalent M-X bonds are present. The latter were represented by the model compounds M(2)(hpp)(4)(H)(2). On the basis of calculations, we estimate the reactions M(2)(hpp)(4) + X(2) to give M(2)(hpp)(4)X(2) to be enthalpically favorable for X = Cl but not for X = H. These results are discussed in terms of the recent work of Cotton and Murillo and our attempts to prepare parallel-linked oligomers of the type [[bridge]-[M(2)]-](n)().     

Synthesis, characterization and photophysics of a new series of anionic C,N,C cyclometalated platinum complexes

A novel series of anionic mononuclear terdentate dicyclometalated complexes (NBu4)[Pt(CwedgeNwedgeC)X] (HCwedgeNwedgeCH=2,6-diphenylpyridine) containing acetylide (X=C[triple bond]CR, R=tBu, 1; Ph, 2; Tol, 3; (4-OMe)C6H4, 4) or another anionic ligand (X=CN, 5; S-2Py, 6; CH2COCH3, 7) have been synthesized and fully characterized. The solid-state structures of complexes 1 and 4-6 have also been determined by X-ray diffraction studies, showing, in all the cases, the presence of several types of weak hydrogen interactions, leading to the generation of supramolecular 2D (1) or 3D (4-6) architectures. All the complexes (1-7) are intensely luminescent at low temperature (solid and glassy CH2Cl2), exhibiting concentration dependence in the emissions of the glassy CH2Cl2 matrix.