Comparison of the Reactivity of Platinum(II) and Platinum(0) Complexes with Iminophosphine and Phosphinocarbonyl Ligands

Isonitrile μ2-carbido complexes

The μ-carbido complex [WPt(μ-C)Br(CO)2(PPh3)2(Tp*)] (Tp = hydrotris(dimethylpyrazolyl)borate) undergoes substitution of one phosphine ligand with isonitriles to afford complexes [WPt(μ-C)Br(CNR)(CO)2(PPh3)(Tp*)] (R = tBu, C6H3Me2-2,6, C6H2Me3-2,4,6). For aryl but not alkyl isocyanides disubstitution follows to afford [WPt(μ-C)Br(CNR)2(CO)2(Tp*)] (R = C6H2Me2-2,6, C6H2Me3-2,4,6). The bis(isonitrile) derivatives, including [WPt(μ-C)Br(CNtBu)2(CO)2(Tp*)], may also be prepared from the reactions of triangulo-[Pt3(CNR)6] with [W(CBr)(CO)2(Tp*)]. Bis- and tris(dimethylpyrazolyl)borate pro-ligand salts replace the bromide and one phosphine in [WPt(μ-C)Br(CNC6H2Me3)(CO)2(PPh3)(Tp*)] or the bromide and one isonitrile in [WPt(μ-C)Br(CNC6H2Me3)2(CO)2(Tp*)] to afford [WPt(μ-C)(CNC6H2Me3)(CO)2(Tp*)(L)] (L = κ2-Tp*, dihydrobis(pyrazolyl)borate). Structural, spectroscopic and computational data for the complexes are discussed to interrogate the nature of the WC-Pt carbido bridge by analogy with a range of other sp-C1 and sp-B1 ligands (CN, CCH, CP, CAs, CSb, CNO, BO, BNH and BCH2).

Symmetric and non-symmetric anthracen-diyl bis(alkylidynes)

Three examples of 9-bromo-10-(alkylidynyl)anthracenes, [W{CC(C₆H₄)₂CBr}(CO)₂(L)] (L = hydrotris(dimethylpyrazol-1-yl)borate Tp*, hydrotris(pyrazol-1-yl)borate Tp, hydrotris(2-mercapto-N-methylimidazol-1-yl)borate Tm) were prepared via modified Fischer-Mayr acyl oxide-abstraction protocols. With a sufficiently bulky ancillary ligand (L = Tp*) the aryl bromide is ammenable to cross-coupling reactions that enable more elaborate derivatives to be prepared. These including symmetric bis(alkylidynyl)anthracenes as well as non-palindromic examples bearing disparate metals and/or co-ligands. In contrast, these couplings fail for smaller ligands (L = Tp, Tm) where it was found that Pd⁰ or Pt⁰ were instead able to coordinate across two WC bonds to give trimetallic bow-tie complexes, [W₂M{μ-CC(C₆H₄)₂CBr}₂(CO)₄(L)₂] (M = Pd, Pt; L = Tp, Tm).

Metal coordination to a dimetallaoctatetrayne

The reactions of the ditungstaoctatetrayne [(Tp*)(CO)₂W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])W(CO)₂(Tp*)] with several metal complexes have been investigated. Addition of [Co₂(CO)₈] occurs across the internal C[triple bond, length as m-dash]C bonds, whereas [AuCl(SMe₂)] initially delivers 'AuCl' across the W[triple bond, length as m-dash]C carbyne bonds before undergoing further reaction to oxidise the tungsten and replace the carbonyl ligands with chloride in [(Tp*)Cl₂W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])WCl₂(Tp*)] with retention of the ditungstaoctatetrayne bridge. Reaction with [AuCl(PR₃)] (R = Ph, Cy) in the presence of AgPF₆ prevents this oxidation and adds [AuPR₃]⁺ across the W[triple bond, length as m-dash]C bonds to give dicationic derivatives. Finally, the reaction with [Pt(nbe)₃] (nbe = norbornene, bicyclo[2.2.1]hept-2-ene) and 1,5-cyclooctadiene (COD) adds a 'Pt(COD)' unit to one or both tungsten-carbon bonds, allowing both the mono- and diplatinum complexes to be isolated.

Morin P, Westcott SA. Synthesis, characterization, and anticancer properties of iminophosphineplatinum(II) complexes containing boronate esters

Three new iminophosphines containing pinacol-derived boronate esters have been prepared and ligated to dichloridoplatinum(II) fragments. All compounds have been characterized fully, including an X-ray diffraction study carried out for the platinum complex 8, which is derived from 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline. These three new platinum complexes, along with the non-boron containing control, have been examined for their initial cytotoxic properties against two glioma cell lines using the MTT method.

Transition metal complexes of the pyridylphosphine ligand o-C6H4(CH2PPy2)2

The synthesis and coordination behaviour of the pyridylphosphine ligand o-C₆H₄(CH₂PPy₂)₂ (Py = 2-pyridyl) are reported. The phosphine selenide was synthesised and the ¹J_PSe value of 738 Hz indicates the phosphorus atoms have a similar basicity to PPh₃. The ligand reacts with platinum(ii) and palladium(ii) complexes to give simple diphosphine complexes of the type [MX₂(PP)] (M = Pt, X = Cl, I, Me, Et; M = Pd, X = Cl, Me). When the ligand is reacted with chloromethyl(hexa-1,5-diene)platinum the [PtClMe(PP)] complex results, from which a series of unsymmetrical platinum complexes of the type [PtMeL(PP)]⁺ (L = PPh₃, PTA, SEt₂ and pyridine) can be made. This enabled the comparison of the cis and trans influences of a range of ligands. The following cis influence series was compiled based on ³¹P NMR data of these complexes: Py ≈ Cl > SEt₂ > PTA > PPh₃. Reaction of [PtClMe(PP)] with NaCH(SO₂CF₃)₂ and carbon monoxide slowly formed an acyl complex, where the CO had inserted in the Pt-Me bond. Attempts to achieve P,P,N chelation, through abstracting the chloride ligand in [PtClMe(PP)], were unsuccessful. When the ligand reacted with platinum(0), palladium(0) and silver(i) complexes the bis-chelated complexes [M(PP)₂] (M = Pt, Pd) and [Ag(PP)₂]⁺ were formed respectively. Reaction of the ligand with [Ir(COD)(μ-Cl)]₂ formed [IrCl(PP)(COD)]. When the chloride ligand was abstracted, the pyridyl nitrogens were able to interact with the iridium centre facilitating the isomerisation of the 1,2,5,6-η⁴-COD ligand to a 1-κ-4,5,6-η³-C₈H₁₂ ligand. The X-ray crystal structure of [Ir(1-κ-4,5,6-η³-C₈H₁₂)(PPN)]BPh₄ confirmed the P,P,N chelation mode of the ligand. In solution, this complex displayed hemilabile behaviour, with the pyridyl nitrogens exchanging at a rate faster than the NMR time scale at room temperature.

Synthesis and catalytic applications of ruthenium(ii)–phosphino-oxime complexes

Ruthenium complexes containing a phosphino-oxime ligand have been synthesized, and their catalytic utility for the rearrangement of aldoximes, as well as for the α-alkylation/reduction of acetophenones with primary alcohols, demonstrated.

Ruthenium(ii) complexes containing a phosphine-functionalized thiosemicarbazone ligand: synthesis, structures and catalytic C–N bond formation reactions via N-alkylation

We report the coordination flexibility of phosphino-thiosemicarbazone in ruthenium(ii) complexes, together with their catalytic properties with regards to N-alkylation.

Bite-angle bending as a key for understanding group-10 metal reactivity of d10-[M(NHC)2] complexes with sterically modest NHC ligands

Experimental and theoretical investigations on the novel 14 VE complexes [M⁰(iPr₂Im)₂] (M = Pd 3, Pt 4; iPr₂Im = 1,3-di-isopropyl-imidazolin-2-ylidene) and a comparison to their Ni congener reveal that NHC–M–NHC angle bending is a key to understand the reactivity of d¹⁰-[M(NHC)₂] complexes.

Synthesis, characterization and investigations on the reactivity of the novel metal basic, yet isolable 14 VE NHC-complexes [M⁰(iPr₂Im)₂] (M = Pd 3, Pt 4; iPr₂Im = 1,3-di-isopropyl-imidazolin-2-ylidene; VE = valence electron; NHC = N-heterocyclic carbene) is reported and compared to the chemistry of the corresponding nickel complex. Quantum chemical analyses reveal that differences in the reactivity of group 10 NHC complexes are caused by differences in the rigidity and thus activation strain associated with bending the corresponding d¹⁰-[M(NHC)₂] fragments during reaction. These results should have implications for the understanding of the fundamental steps in catalytic cycles, in which such complex fragments are employed.

Efficient and versatile catalysis of N-alkylation of heterocyclic amines with alcohols and one-pot synthesis of 2-aryl substituted benzazoles with newly designed ruthenium(ii) complexes of PNS thiosemicarbazones

Efficient catalytic N-alkylation of amines using Ru(ii) catalysts with good yields and high selectivity.

Synthesis of new late transition metal P,P-, P,N-, and P,O- complexes using phosphonium dimers as convenient ligand precursors

The phosphonium dimer [-Cy2PCH(OH)CH2-]2(X)2, X = Cl(-), Br(-) was used to synthesize and characterize a variety of late transition metal complexes containing chelating phosphino-enolate (PCy2CH═CHO(-)), imine (PCy2CH2CH═NR, R = Ph, (S)-CHMePh), and oxime (PCy2CH2CH═NOH) ligands. The phosphonium dimer, when deprotected with base, generates the phosphine aldehyde PCy2CH2CHO in situ, which, in the presence of [M(COD)Cl]2, M = Rh, Ir, and a PF6(-) salt, or [Ni(H2O)6][BF4]2, facilitates a condensation reaction with an amine or hydroxylamine to form phosphino-imine or phosphino-oxime metal complexes [M(COD)(P-N)][PF6] or [Ni(P-N)2][X]2, X = ClO4(-), BF4(-), respectively. In the absence of an amine, phosphino-enolate containing complexes are formed. A neutral Ni(II) complex Ni(PCy2CH═CHO)2 with trans-bis(phosphino-enolate) ligands which resemble ligands used on nickel for olefin oligomerization, as well as neutral Rh(I) and Ir(I) 1,5-cyclooctadiene complexes M(COD)(PCy2CH═CHO) are characterized. Both the rhodium and iridium complexes are active olefin hydrogenation catalysts. Reaction of the phosphino-aldehyde with Pt(COD)Cl2 results in the formation of trans-PtCl2(PCy2CH2CHO)2 with pendant aldehyde groups, and under certain conditions, they undergo an intraligand aldol condensation to form a disphosphine ligand.

Dichlorido{N-[2-(diphenylphosphanyl)benzylidene]-2-methylaniline}palladium(II) acetonitrile monosolvate

The title imino–phosphine compound, [PdCl2(C26H22NP)]·CH3CN, was prepared by reaction ofN-[2-(diphenylphosphanyl)benzylidene]-2-methylaniline with dichlorido(cycloocta-1,5-diene)palladium(II) in dry CH2Cl2. The PdIIcation is coordinated by the P and N atoms of the bidentate chelating ligand and by two chloride anions, generating a distorted square-planar coordination geometry. There is a detectabletransinfluence for the chloride ligands. The methyl group present in this structure has an influence on the crystal packing.