Martin A. Bennett

Recent advances in the chemistry of arene complexes of ruthenium(0) and ruthenium(II)

Abstract Aspects of the chemistry of arene complexes of ruthenium and osmium in zero and +2 oxidation states are reviewed, with emphasis on the formation of isomeric endo- and exo-o-xylylene complexes of ruthenium(0) and osmium(0) from 1,2-dimethylarene complexes of the divalent metals, and on the stoichiometric and catalytic chemistry of a labile naphthalene complex of ruthenium(0).

Arene ruthenium(II) complexes formed by dehydrogenation of cyclohexadienes with ruthenium(III) trichloride

Arenedi-µ-chloro-ruthenium complexes [RuCl2(arene)]2 have been prepared by dehydrogenation of the appropriate cyclohexa-1,3-diene or cyclohexa-1,4-diene with ethanolic ruthenium(III) trichloride. They react with ligands (L) such as pyridine, tertiary phosphines, or tertiary arsines to give monomeric complexes [RuCl2(arene)L], which are formally analogous to the arenetricarbonylchromium complexes. Analogous dibromo-, di-iodo-, halogeno-(methyl), and dimethyl derivatives have also been prepared; the latter are thermally unstable and air-sensitive. Reaction of the complexes [RuCl2(arene)]2(arene = benzene or p-cymene) with water gives binuclear tri-µ-chloro-cationic species [Ru2C13(arene)2]+, and reaction with silver(I) tetrafluoroborate in acetonitrile gives monomeric [Ru(arene)(MeCN)3]2+. I.r. and n.m.r. data for the new complexes are given. The complexes [RuCl2(arene)L](L = PBun3 or PPh3) undergo partial or complete arene exchange on heating or on u.v. irradiation in an aromatic solvent, co-ordinated p-cymene being the most easily displaced. The exchange method can be used to prepare hexamethylbenzene complexes, e.g.[RuCl2(C6Me6)(PBun3)]. The results are compared with available data on arene exchange in arenetricarbonylchromium complexes and discussed in terms of electronic and steric effects on metal–arene bonding.

Methyl- and phenyl-bis(tertiary phosphine) hydroxo complexes of platinum(II): Reactions with weak acids and hydration of nitriles catalysed by hydroxo and N-bonded carboxamido complexes of platinum(II)

Abstract Methyl- and phenyl-hydroxo complexes of platinum(II), Pt(OH)RL2 (R = Ph, L = Pcy3, P-t-Bu2Me, P-t-BuMe2, PEt3, PMePh2, PMe2Ph; R = Me, L = P-t-Bu2Me, P-i-Pr3) have been prepared by the action of KOH on cationic acetone complexes [PtR(OCMe2)L2]+ generated in situ. All have mutually trans-phosphine ligands, except for Pt(OH)Ph(PMe2Ph)2, which was isolated in an impure state as a cis-trans mixture. The hydroxo complexes behave as strong bases and react with nitromethane, acetone or p-cresol to give, respectively, C-bonded nitromethyl-(CH2NO2), C-bonded acetonyl-(CH2COMe) and O-bonded p-cresolato-(p-MeC6H4O) platinum(II) complexes. Complexes in the first two of these classes can also be obtained in lower yield by reaction of PtClRL2 with nitromethane or acetone in the presence of silver oxide. Methyl cyanoacetate, NCCH2CO2Me, reacts with Pt(OH)PhL2 (L = PEt3, P-t-Bu2Me) to give N-bonded methoxycarbonyl-keteniminato complexes Pt(NCCHCO2Me)PhL2, but with Pt(OH)Me(dppp) the product is the C-bonded cyano(methoxycarbonyl)methyl complex Pt[CH(CN)(CO2Me)]Me(dppp). Both hydroxo complexes and N-bonded acetamido complexes Pt(NHCOMe)RL2 catalyse hydration of acetonitrile to acetamide at 80°C, but are less efficient than trialkylphosphine platinum(0) complexes. The order of activity for R = Ph is L = PEt3 > P-t-BuMe2 > PPh3 ∼ PMe2Ph > P-t-Bu2Me >> Pcy3, while for a given tertiary phosphine the order of activity is R =, Ph > Me. Hydration of acrylonitrile under similar conditions generally gives a mixture of acrylamide, β-cyanoethanol and ββ-dicyanoethyl ether, the last two products arising in irreproducible amounts by addition of water to the olefinic double bond. The mechanisms of these reactions are discussed in the light of the observed trends.

A simple preparation of bis-arene-ruthenium cationic complexes, including those containing different arenes

Abstract Bis-η 6 -arene-ruthenium(II) salts of general formula [Ru(arene 1 )(arene 2 )]Y 2 (arene 1 = benzene, mesitylene or hexamethylbenzene, arene 2 = a wide range of aromatic compounds and Y = BF 4 or PF 6 ) can be prepared in moderate to high yields by treatment of [RuCl 2 (η 6 -arene 1 )] 2 in acetone successively with AgBF 4 or AgPF 6 , acid (CF 3 CO 2 H, HBF 4 or HPF 6 ) and arene 2 .

Tridentate chelate π-bonded complexes of rhodium(I), iridium(I), and iridium(III) and chelate σ-bonded complexes of nickel(II), palladium(II), and platinum(II) formed by intramolecular hydrogen abstraction reactions

Abstract 2,2′-Bis(o-diphenylphosphino)bibenzyl, o-Ph2PC6H4CH2CH2C6H4PPh2-o (bdpbz), is dehydrogenated by various rhodium complexes to give the planar rhodium(I) complex , from which the ligand, 2,2′-bis(o-diphenylphosphino)-trans-stilbene (bdpps) can be displaced by treatment with sodium cyanide. The stilbene forms stable chelate olefin complexes with planar rhodium(I) and iridium(I) and with octahedral iridium(III). On reaction with halide complexes of nickel(II), palladium(II) or platinum(II), the stilbene ligands (R  Ph or o-CH3C6H4) lose a vinyl proton in the form of hydrogen chloride to give chelate, planar σ-vinyls of general formula MX(o-R 2 PC 6 H 4 C CHC6H4PR2-o) (M  Ni, Pd, Pt; X  Cl, Br, I) of high thermal stability; analogous methyl derivatives Pt(CH 3 )(o-R 2 PC 6 H 4 C CHC6H4PR2-o) are obtained from Pt(CH3)2(COD) (COD  1,5-cyclooctadiene) and the stilbene ligands. The bibenzyl also forms chelate σ-benzyls MX(o-Ph 2 PC 6 H 4 C HCH2C6H4PPh2-o) (M  Pd, Pt; X  Cl, Br, I). The 1H NMR spectra of the o-tolyl methyl groups in the compounds MX(o-R 2 PC 6 H 4 C CHC6H4PR2-o) (M  Ni, Pd, Pt; R  o-CH3C6H4) vary with temperature, probably as a consequence of interconversion of enantiomers arising from restricted rotation about the MP and MC bonds. Possible mechanisms for the dehydrogenation reactions are briefly discussed.

Preparation and X-ray structure of a platinum(II) hydroxycarbonyl, Pt(CO2H){C6H3(CH2PPh2) 2-2,6}, containing a trans-spanning, tridentate P,C,P-ligand

Abstract The ligand 1,3-{bis(diphenylphosphino)methyl}benzene, 1,3-C6H4(CH2PPh2)2 (3a) undergoes cyclometallation on heating in 2-methoxyethanol either with PtCl(CH3)(COD) or, in the presence of 2-methylaminoethanol, with PtCl2(COD) to give PtCl{C6H3(CH 2PPh2)2-2,6} (6). In this complex, the tridentate anionic ligand C6H3(CH2PPh2)2-2,6 (2a) is attached to platinum via a σ-bonded carbon atom and mutually trans-phosphorus atoms. Successive treatment of 6 with AgBF4 and KOH gives the hydroxo-complex Pt(OH)(2a) (11), which reacts with CO to give the corresponding hydroxycarbonyl Pt(CO2H)(2a) (12). The structure of 12 · 1.5C6H6 was determined by X-ray diffraction methods and shown to consist of a dimer in which two planar trans-pt(CO2H)(2a) units are joined by hydrogen-bonded carboxylate groups. The hydrogen-bonded O⋯O distance [2.750(4)A] is significantly larger than that in trans-pt(CO2H)(C6H5)(PEt3)2 (1) [2.695(8)A], which may be related to the greater tendency of 2a to form a monomer in dichloromethane.

Unprecedented near-infrared (NIR) emission in diplatinum(III) (d7-d7) complexes at room temperature.

The synthesis and single-crystal X-ray structures of the first family of efficient NIR emitters with tunable emission energy based on dihalodiplatinum(III) (5d(7)-5d(7)) complexes of general formulae [Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)X(2)] (R = Me or CHMe(2); X = Cl, Br or I), together with that of their diplatinum(II) (5d(8)-5d(8)) precursors ([Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)]) and cyano counterparts (X = CN), are reported. The diplatinum(II) complexes with isopropyl groups are isolated initially as a mixture of two species, one being a half-lantern structure containing two bridging and two chelate C(6)H(3)-5-CHMe(2)-2-AsPh(2) ligands (1b) that exists in two crystalline modifications [d(Pt...Pt) = 3.4298(2) A and 4.3843(2) A]; the other is a full-lantern or paddle-wheel structure having four bridging C(6)H(3)-5-CHMe(2)-2-AsPh(2) ligands (2b) [d(Pt...Pt) = 2.94795(12) A]. Complete conversion of the isomers into 2b occurs in hot toluene. The Pt-Pt bond distances in the diplatinum(III) complexes are less than that in 2b and increase in the order X = Cl (3b) [2.6896(2) A] < Br (4b) [2.7526(3) A] < I (5b) [2.7927(7) A] approximately CN (6b) [2.7823(2), 2.7924(2) A for two independent molecules]. Comparison with the corresponding data for our previously reported series of complexes 3a-6a (R = Me) indicates that the Pt-Pt bond lengths obtained from single-crystal X-ray analysis are influenced both by the axial ligand and by intermolecular lattice effects. Like [Pt(2)(mu-pop)(4)](4-) [pop = pyrophosphite, (P(2)O(5)H(2))(2-)], the diplatinum(II) complexes [Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)] [R = Me (2a), CHMe(2) (2b)] display intense green phosphorescence, both as solids and in solution, and at room temperature and 77 K, with the emission maxima in the range 501-532 nm. In contrast to the reported dihalodiplatinum(III) complexes [Pt(2)(mu-pop)(4)X(2)](4-) that exhibit red luminescence only at 77 K in a glass or as a solid, complexes 3a-6a and 3b-6b are phosphorescent in the visible to near-infrared region at both room and low temperatures. The electronic spectra and photoemissive behavior are discussed on the basis of time-dependent density functional theory (TDDFT) calculations at the B3YLP level. The photoemissive states for the halide analogues 3a,b-5a,b involve a moderate to extensive mixing of XMMCT character and MC [d sigma-d sigma*] character, whereas the cyano complexes 6a and 6b are thought to involve relatively less mixing of the XMMCT character into the MC [d sigma-d sigma*] state.

Areneruthenium(II) carboxylates: reactions with ligands and the X-ray structure of the p-cymene pyrazine complex [Ru(η-p-MeC6H4CHMe2)Cl(pyz)2]PF6

The preparation of monomeric areneruthenium(II) acetates and trifluoroacetates [Ru(η-arene)X(O2CR)] and [Ru(η-arene)(O2CR)2](X = Cl or Br; R = Me or CF3; arene = C6H6, p-MeC6H4CHMe2, C6H3Me3-1,3,5, C6H2Me4-1,2,4,5, or C6Me6)(not all possible combinations) from the corresponding dihalides [{Ru(η-arene)X2}2] is described. Infrared spectra suggest that the complexes [Ru(η-arene)X(O2CR)] contain a bidentate carboxylate group and that [Ru(η-arene)(O2CR)2] contain one bi- and one uni-dentate carboxylate group, which are apparently equivalent on the n.m.r. time-scale at room temperature. Reaction of trifluoroacetic acid with [{Ru(η-C6Me6)Cl2}2] gives a complex of empirical formula Ru(η-C6Me6)Cl(O2CCF3)·CF3CO2H which may be a salt [(η-C6Me6)Ru(η-Cl)2(µ-O2CCF3)Ru(η-C6Me6)][H(O2CCF3)2]·CF3CO2H. Triphenylphosphine converts [Ru(η-C6Me6)(O2CR)2](R = Me or CF3) into [Ru(η-C6Me6)(O2CR)2(PPh3)] in which both carboxylate groups are unidentate. The trifluoroacetate group is completely displaced from [Ru(η-C6H6)Cl(O2CCF3)] by pyridine (py) or ethyldiphenylphosphine to give [Ru(η-C6H6)ClL2]+(L = py or PEtPh2), isolated as PF6– or BPh4– salts. The potentially binucleating ligands pyrazine (pyz), 4,4′-bipyridyl, and 1,3-dithiane react either with [Ru(η-C6H6)Cl(O2CCF3)] or with [{M(η-p-MeC6H4CHMe2)Cl2}2](M = Ru or Os) in the presence of NH4PF6 or NaBPh4 in methanol to give [M(η-arene)ClL2]+ salts in which only one donor atom of the ligand is co-ordinated, but pyz and [{Ru(η-p-MeC6H4CHMe2)Cl2}2] react in dry tetrahydrofurane to give the pyrazine-bridged species {Ru(η-p-MeC6H4CHMe2)Cl2}2(µ-pyz). The structure of the complex [Ru(η-p-MeC6H4CHMe2)Cl(pyz)2]PF6 has been verified by X-ray analysis. The crystals are triclinic, space group P, with a= 9.265(2), b= 9.684(4), c= 12.969(2)A, α= 86.51(2), β= 72.89(2), and γ= 85.59(2)°.

Insertions of unsymmetric alkynes into the metal-carbon bonds of nickelacycles: What determines the regiochemistry?

Although the insertion of alkynes into transition-metal−carbon bonds plays an important role in synthesis, the regioselectivities observed with unsymmetric alkynes have usually been interpreted on the basis of steric effects. In this perspective paper, we review the available data for such reactions with nickelacycles and present the results of some preliminary theoretical (DFT) calculations. These suggest that, even for unactivated alkynes, the regiochemistry may also be controlled by electronic factors such as frontier-orbital interactions between the triple-bond of the alkyne and the polarized metal−carbon bond.

Mono-cyclooctyne complexes of divalent and tetravalent molybdenum and tungsten

Abstract Cyclooctyne (C 8 H 12 ) reacts with the dialkyldithiocarbamato complexes Mo(S 2 CNR 2 ) 2 (CO) 2 (PPh 3 ) and W(S 2 CNR 2 ) 2 (CO) 3 (R = Me, Et) in a 1:1 mol ratio to give the divalent metal alkyne complexes M(S 2 CNR 2 ) 2 (CO)(C 8 H 12 ). These are oxidized by bromine or iodine to tetravalent metal alkyne complexes MX 2 (S 2 CNR 2 ) 2 (C 8 H 12 ) (M = Mo, W; X = Cl, Br; R = Me, Et). Carbon-13 NMR and IR spectroscopic data indicate that in these compounds and in the triethylphosphine complexes MBr 2 (CO)C 8 H 12 )(PEt 3 ) 2 (M = Mo, W) cyclooctyne behaves as a 4π-electron donor, whereas in the oxomolybdenum(IV) cyclooctyne complexes MoO(S 2 CNR 2 ) 2 C 8 H 12 ) (R = Me, Et) it donates approximately π-electrons owing to competing π-donation from the oxo ligand.