Poly(imidazolyliden-yl)borato Complexes of Tungsten: Mapping Steric vs. Electronic Features of Facially Coordinating Ligands.

A convenient synthesis of [HB(HImMe)3](PF6)2 (ImMe = N-methylimidazolyl) is decribed. This salt serves in situ as a precursor to the tris(imidazolylidenyl)borate Li[HB(ImMe)3] pro-ligand upon deprotonation with nBuLi. Reaction with [W(≡CC6H4Me-4)(CO)2(pic)2(Br)] (pic = 4-picoline) affords the carbyne complex [W(≡CC6H4Me-4)(CO)2{HB(ImMe)3}]. Interrogation of experimental and computational data for this compound allow a ranking of familiar tripodal and facially coordinating ligands according to steric (percentage buried volume) and electronic (νCO) properties. The reaction of [W(≡CC6H4Me-4)(CO)2{HB(ImMe)3}] with [AuCl(SMe2)] affords the heterobimetallic semi-bridging carbyne complex [WAu(µ-CC6H4Me-4)(CO)2(Cl){HB(ImMe)3}].

Manuka Oil-A Review of Antimicrobial and Other Medicinal Properties.

Manuka oil is an essential oil derived from Leptospermum scoparium, a plant that has been used by the indigenous populations of New Zealand and Australia for centuries. Both the extracted oil and its individual components have been associated with various medicinal properties. Given the rise in resistance to conventional antibiotics, natural products have been targeted for the development of antimicrobials with novel mechanism of action. This review aimed to collate available evidence on the antimicrobial, anti-parasitic and anti-inflammatory activities of manuka oil and its components. A comprehensive literature search of was conducted using PubMed and Embase (via Scopus) targeting articles from database inception until June 2020. Chemical structures and IUPAC names were sourced from PubChem. Unpublished information from grey literature databases, Google search, targeted websites and Google Patents were also included. The present review found extensive in vitro data supporting the antimicrobial effects of manuka oil warrants further clinical studies to establish its therapeutic potential. Clinical evidence on its efficacy, safety and dosing guidelines are necessary for its implementation for medical purposes. Further work on regulation, standardization and characterization of the medicinal properties of manuka oil is required for establishing consistent efficacy of the product.

In Search of Fulminate Analogues: Ln M≡CP=NR.

The "CPNR" ligand may be viewed as being isolobal with fulminate, CNO; however, attempts to prepare a complex of such a ligand resulted instead in a range of novel imino and aminophosphinocarbyne complexes. Sequential treatment of [Mo(≡CBr)(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) with nBuLi and ClP=NMes* (Mes*=C6 H2 tBu3 -2,4,6) afforded mixtures of the complexes [Mo(≡CPnBuNHMes*)(CO)2 (Tp*)] and traces of the bimetallic products [Mo2 {µ2 -C2 P2 O(NHMes)2 }(CO)4 (Tp*)2 ] and [Mo2 (µ2 -C2 PNHMes)(CO)4 (Tp*)2 ]. The reaction of [W(≡CBr)(CO)2 (Tp*)] with nBuLi and ClP=NMes* afforded predominantly the mononuclear carbyne [W{≡CP(=NMes*)nBu2 })(CO)2 (Tp*)] and traces of the binuclear complex [W2 (µ-C2 PNHMes)(CO)4 (Tp*)2 ] which is also obtained when tBuLi is used. Although not isolable, the intended complexes [M(≡CPNMes*)(CO)2 (Tp*)] could be generated in situ and spectroscopically characterized via the reactions of the stannyl carbynes [M(≡CSnnBu3 )(CO)2 (Tp*)] and ClP=NMes*. The preceding observations are mechanistically interpreted with reference to a computational interrogation of the model complex [Mo(≡CP=NCH3 )(CO)2 (Tp*)], the LUMO of which has considerable phosphorus character.

Semi-bridging σ-silyls as Z-type ligands.

The reactions of SiHPh(NCH2PPh2)2C6H4-1,2 with a range of zerovalent group 10 reagents afford the homoleptic bimetallic complexes [M2{µ-κ3-Si,P,P'-SiPh(CH2PPh2)2C6H4}2] (M = Ni, Pd, Pt) in which the M-M bond is unsymmetrically bridged by two σ-silyl groups. The asymmetry of the M2Si2 core increases from Ni through Pd to Pt and is consistent with a bonding description in which one metal acts as an electron pair donor to a trigonal bipyramidal 'Z-type' silicon centre, reminsicent of semi-bridging coordination by CO, carbynes and boryl ligands.

Hydrogenating an organometallic carbon chain: buten-yn-diyl (CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C) as a missing link.

The sequential reaction of [Ru(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] with [Ru(CO)2(PPh3)3], and N-chlorosuccinimide affords the binuclear tetracarbido complex [Ru2(µ-C[triple bond, length as m-dash]CC[triple bond, length as m-dash]C)Cl2(CO)4(PPh3)4]. This may be compared with the first example of a butenyndiyl bridged bimetallic complex [Ru2(µ-CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C)Cl2(CO)4(PPh3)4] which is obtained from the reaction of [Ru(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] with [RuHCl(CO)(PPh3)3] followed by carbonylation. Characterisational data are discussed with reference to constituent model complexes [Ru(C[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] and [Ru(CH[double bond, length as m-dash]CH2)Cl(CO)2(PPh3)2] in addition to DFT analysis of the bonding in the complexes [Ru2(µ-L)Cl2(CO)4(PMe3)4] (L = C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C, CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C, CH[double bond, length as m-dash]CH-CH[double bond, length as m-dash]CH). A range of other tetracarbido complexes which may be prepared from [RuCl(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)(CO)2(PPh3)2] is also described and includes [RuAu(µ-C4)Cl(CO)3(PPh3)3], [RuIr(µ-C4)Cl(CO)3(PPh3)4], [RuIr(µ-C4)H(NCMe)(CO)3(PPh3)4]BF4, [RuIr(µ-C4)Cl(η2-O2)(CO)3(PPh3)4], [Ru2Hg(µ-C4)2Cl2(CO)4(PPh3)4], [Ru2Pt(µ-C4)2Cl2(CO)4(PPh3)6] and [Ru2(µ-C4)HCl(CO)4(PPh3)4].

Bis(alkylidynyl)tellurides and ditellurides.

The tellurocarbonylates [M(CTe)(CO)2(Tp*)]- (M = Mo, W; obtained from [M([triple bond, length as m-dash]CBr)(CO)2(Tp*)] and Li2Te or [M([triple bond, length as m-dash]CLi)(CO)2(Tp*)] and Te) react with an additional equivalent of [M([triple bond, length as m-dash]CBr)(CO)2(Tp*)] to give bis(alkylidynyl)tellurides, [M2(µ-CTeC)(CO)4(Tp*)2], whilst oxidation with [Fe(η-C5H5)2]PF6 affords the corresponding ditellurides [M2(µ-CTe2C)(CO)4(Tp*)2]. The unprecedented M[triple bond, length as m-dash]CTeC[triple bond, length as m-dash]M and M[triple bond, length as m-dash]CTe2C[triple bond, length as m-dash]M bridges are discussed with reference to more conventional but rare alkylidynyltelluroethers [M([triple bond, length as m-dash]CTeR)(CO)2(Tp*)] (R = Me, nBu, Ph).

Dihydrobis(methimazolyl)borato complexes of ruthenium and osmium.

The reaction of Na[H2B(mt)2] (mt = 2-mercapto, 3-methylimidazol-1-yl, methimazolyl) with [Ru(X)Cl(CO)(PPh3)n] (n = 3 X = H; n = 2 BO2C6H4, SiCl3, SiMe3) affords the complexes [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}]. Evidence is presented to also support the transient formation of [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] (X = CH[double bond, length as m-dash]CHPh, Ph) via a similar strategy, although these are unstable. The osmium complex [OsH(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] is similarly obtained from [OsHCl(CO)(PPh3)3] or [OsH(NCMe)2(CO)(PPh3)2]BF4. The reaction of [RuH(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] with chloroform or diphenyldiselenide provides [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] (X = Cl, SePh), the latter reaction also providing traces of [Ru(SeH)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}]. Spectroscopic and structural data for the series [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] are discussed in terms of perturbations on the B-H-Ru interaction by the trans-ligand X.

Rearrangement of bis(alkylidynyl)phosphines to phospha-acyls.

A range of bis(alkylidynyl)phosphines RP{C[triple bond, length as m-dash]M(CO)2(Tp*)}2 (M = Mo, W; R = Cl, Ph, Cy; Tp* = hydrotris(dimethylpyrazolyl)borate) are obtained from the reactions of [M([triple bond, length as m-dash]CLi)(CO)2(Tp*)] with Cl2PR or alternatively via the palladium(0)-mediated reactions of [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] with RPH2 (R = Py, Cy). The complexes RP{C[triple bond, length as m-dash]W(CO)2(Tp*)}2 rearrange slowly (R = Cl) or on heating (R = Ph) to afford the isomeric phospha-acyls [W2(µ:η1-C;η2-C,P-CCPR)(CO)4(Tp*)2].

Mono(imidazolin-2-iminato) titanium complexes for ethylene polymerization at low amounts of methylaluminoxane.

The polymerization of ethylene with titanium complexes bearing one bulky imidazolin-2-iminato ligand (L) in the presence of MAO and/or TTPB as cocatalysts have been explored. The complex LTiCl3 and its methylated forms were prepared to shed light on the nature of the active polymerization species. With some of these complexes, the best catalytic activity was obtained at an Al:Ti ratio of 8.

A golden ring: molecular gold carbido complexes.

Stannylcarbynes [M(≡CSnMe3)(CO)2(Tp*)] [M = Mo, W; Tp* = hydrotris(dimethylpyrazol-1-yl)borate], which are readily obtained via the successive treatment of [M(≡CBr)(CO)2(Tp*)] with (n)BuLi and ClSnMe3, serve as effective carbyne transmetalation agents for the preparation of heteronuclear molecular gold carbido complexes such as [M(≡CAuPPh3)(CO)2(Tp*)] and the tetrameric golden ring complex [W(≡CAu)(CO)2(Tp*)]4, which are in turn able to transfer the carbido unit to palladium.

Bis(1,3-di-tert-butylimidazolin-2-iminato) titanium complexes as effective catalysts for the monodisperse polymerization of propylene.

The use of bis(1,3-di-tert-butylimidazolin-2-iminato) titanium dichloride (1) and dimethyl (2) complexes in the polymerization of propylene is presented. The complexes were activated using different amounts of methylalumoxane (MAO), giving in each case a very active catalytic mixture and producing polymers with a narrow molecular weight distribution (polydispersity = 1.10). The use of the cocatalyst triphenylcarbenium (trityl) tetra(pentafluorophenyl)borate totally inhibits the reaction, producing the corresponding bis(1,3-di-tert-butylimidazolin-2-iminato) titanium(III) methyl complex, the trityl radical ((•)CPh(3)), the anionic MeB(C(6)F(5))(4)(-), B(C(6)F(5))(3), and the bis(1,3-di-tert-butylimidazolin-2-iminato) titanium(IV) dimethyl·B(C(6)F(5))(3) complex. The use of a combination of physical methods such as NMR, ESR-C(60), and MALDI-TOF analyses enabled us to propose a plausible mechanism for the polymerization of propylene, presenting that the polymerization is mainly carried out in a living fashion. In addition, we present a slow equilibrium toward a small amount of a dormant species responsible for 2,1-misinsertions and chain transfer processes.

Synthetic and computational studies of the palladium(IV) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination.

Synthetic routes to methyl(aryl)alkynylpalladium(IV) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C≡CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C≡CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6); R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C≡CR above ~-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C≡CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(‡) 64 ± 2 kJ mol(-1), ΔS(‡)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(‡) 66 ± 3 kJ mol(-1), ΔS(‡)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC≡CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C≡C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC≡C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).

Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes.

Reductive elimination of C-Cl and C-C bonds from binuclear organopalladium complexes containing Pd-Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(µ-O(2)CMe)](2) (L = benzo[h]quinolinyl) (I), is examined for C-Cl coupling, and the proposed cation, [(L-C,N)PhPd(1)(µ-O(2)CMe)(2)Pd(2)(L-C,N)](+) (II), examined for C-C coupling together with (L-C,N)PhPd(1)(µ-O(2)CMe)(2)Pd(2)Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd(2) to form II is predicted to be favored. Cation II undergoes Ph-C coupling at Pd(1) with concomitant Pd(1)-Pd(2) lengthening and shortening of the Pd(1)-O bond trans to the carbon atom of L; natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the d(x(2)-y(2)) orbital of Pd(1) and population of the d(z(2)) orbitals of Pd(1) and Pd(2) as the Pd-Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C-Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the d(x(2)-y(2)) orbital of Pd(1) with Pd(1)-O(1) lengthening, significantly less population occurs for the d(z(2)) orbital of Pd(1) than for the dissociative pathway, and d(z(2)) at Pd(2) is only marginally populated resulting in an intermediate that is formally a Pd(1)(I)-Pd(2)(III) species, (L-Cl-N,Cl)Pd(1)(µ-O(2)CMe)Pd(2)Cl(O(2)CMe)(L-C,N) that releases chloride from Pd(2) with loss of Pd(I)-Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C-C coupling from III, in this case involving decreased population of the d(z(2)) orbital of Pd(2) and strengthening of the Pd(I)-Pd(III) interaction in the analogous intermediate with η(2)-coordination at Pd(1) by L-Ph-N, C(1)-C(2).

Organoactinides promote the dimerization of aldehydes: scope, kinetics, thermodynamics, and calculation studies.

Surprising catalytic activities have been found for the actinide complexes Cp*(2)ThMe(2) (1), Th(NEtMe)(4) (2), and Me(2)SiCp''(2)Th(C(4)H(9))(2) (3) toward oxygenated substrates. During the catalytic dimerization of benzaldehydes to their corresponding esters, complexes 1 and 2 gave 65 and 85% yield in 48 h, respectively, while the geometry-constrained complex 3 gave 96% yield in 24 h. Exploring the effect of substituents on benzaldehyde, it has been found that, in general, electron-withdrawing groups facilitate the reaction. Kinetic study with complexes 1 and 3 reveals that the rate of the reaction is first order in catalyst and substrate, which suggests the rate equation "rate = k[catalyst](1)[aldehyde](1)". The activation energy of the reaction was found to be 7.16 ± 0.40 and 3.47 ± 0.40 kcal/mol for complexes 1 and 3 respectively, which clearly indicates the advantage of the geometry-constrained complex. Astonishing are the reactivity of the organoactinide complexes with oxygen-containing substrates, and especially the reactivity of complex 3, toward the dimerization of substrates like p-methoxybenzaldehyde, m/p-nitrobenzaldehyde, and furanaldehyde and the reactivity toward the polymerization of terephthalaldehyde. Density functional theory mechanistic study reveals that the catalytic cycle proceeds via an initially four-centered transition state (+6 kcal/mol), followed by the rate-determining six-centered transition state (+13.5 kcal/mol), to yield thermodynamically stable products.

Ligand effects in bimetallic high oxidation state palladium systems.

Ligand effects in bimetallic high oxidation state systems containing a X-Pd-Pd-Y framework have been explored with density functional theory (DFT). The ligand X has a strong effect on the dissociation reaction of Y to form [X-Pd-Pd](+) + Y(-). In the model system examined where Y is a weak σ-donor ligand and a good leaving group, we find that dissociation of Y is facilitated by greater σ-donor character of X relative to Y. We find that there is a linear correlation of the Pd-Y and Pd-Pd bond lengths with Pd-Y bond dissociation energy, and with the σ-donating ability of X. These results can be explained by the observation that the Pd d(z(2)) population in the PdY fragment increases as the donor ability of X increases. In these systems, the Pd(III)-Pd(III) arrangement is favored when X is a weak σ-donor ligand, while the Pd(IV)-Pd(II) arrangement is favored when X is a strong σ-donor ligand. Finally, we demonstrate that ligand exchange to form a bimetallic cationic species in which each Pd is six-coordinate should be feasible in a high polarity solvent.

Binuclear intermediates in oxidation reactions: [(Me(3)SiC[triple bond]C)Me(2)(bipy)Pt-PtMe(2)(bipy)](+) in the oxidation of Pt(II)Me(2)(bipy) (bipy = 2,2'-bipyridine) by IPh(C[triple bond]CSiMe(3))(OTf) (OTf = triflate).

A study of the reaction of PtMe(2)(bipy) with IPh(C[triple bond]CSiMe(3))(OTf) at low temperature in acetone, leading to detection of the Pt-Pt-bonded cation [Pt(2)Me(4)(C[triple bond]CSiMe(3))(bipy)(2)](+), an intermediate in the oxidation of Pt(II) to Pt(IV), is reported. The cation is assessed as Pt(III)-Pt(III) <--> Pt(IV)-Pt(II), and at the other extreme may be regarded as a cationic alkynylplatinum(IV) center, "[Pt(IV)Me(2)(C[triple bond]CSiMe(3))(bipy)](+)", stabilized by "Pt(II)Me(2)(bipy)" as a donor ligand. The detection and isolation of the [Pt(2)Me(4)(C[triple bond]CSiMe(3))(bipy)(2)](+) cation provides a number of insights into the mechanisms of oxidation reactions.