Secondary Phosphine Complexes Research Articles

Pitfalls for POCOP-Type Palladium Pincer Complexes in Catalytic Reduction of CO2 with Catecholborane

Reduction of CO2 with catecholborane (HBcat) is known to be catalyzed by nickel hydride complexes supported by a bis(phosphinite)-based or POCOP-type pincer ligand. The objective of this research is to examine how changing the metal center from nickel to palladium would impact the outcome of CO2 reduction. Stoichiometric studies show that the palladium hydride complexes react rapidly with CO2, although the resulting palladium formate complexes can lose CO2 under reduced pressure or in chloroform. In the presence of HBcat, the formate complexes are converted back to the palladium hydride species while the formate group is reduced to CH3OBcat. This process is also accompanied by the formation of palladium bis(catecholato)borate complexes, which diverts some of the HBcat to yield B2(cat)3 and B2H6. For palladium hydrides stabilized by a POCOP-pincer ligand with relatively small phosphorus substituents (e.g., isopropyl or cyclopentyl groups), HBcat cleaves the P–O bonds in the ligand backbone to degrade the catalysts to secondary phosphine complexes. Without CO2, HBcat also undergoes H2 elimination with the Pd–H moiety to form palladium boryl complexes. These side reactions with HBcat and the palladium pincer complexes play profound roles in the catalytic reduction of CO2 with the borane.

Mild intramolecular P–C(sp3) bond cleavage in bridging diphosphine complexes of RuII RhIII and IrIII

Three new carboxylic acid functionalised diphosphines, R2PCH2N(Ar)CH2PR2 [CyL1 R = Cy, Ar = (1-CO2H)(3-OMe)C6H3, CyL2 R = Cy, Ar = (1-CO2H)(3-OH)C6H3 and PhL3 R = Ph, Ar = (1-CO2H)(5-OMe)C6H3] have been prepared from condensation of R2PCH2OH and the appropriate aromatic amine in MeOH, and isolated as colourless solids (for CyL1, CyL2) in good yield. Reaction of CyL1, CyL2, or PhL3, along with the previously reported diphosphines PhL1, PhL2, and PhL4, and [RuCl(μ-Cl)(η6-Me2CHC6H4Me)]2 in CH2Cl2 affords the P/P-bridging dinuclear ruthenium(II) complexes {RuCl2(η6-Me2CHC6H4Me)}2(μ-CyL1−PhL4) 1a−f as red/orange solids. Careful monitoring by 31P{1H} NMR spectroscopy of CDCl3 solutions of 1a−e revealed remarkably clean P−Csp3 bond cleavage to give RuII mononuclear species 2a−e and the known secondary phosphine complexes RuCl2(η6-Me2CHC6H4Me)(PCy2H) 3 and RuCl2(η6-Me2CHC6H4Me)(PPh2H) 4. Furthermore, facile P−Csp3 bond cleavage of PhL1 can be observed using the chloro-bridged dimers [IrCl(μ-Cl)(η5-C5Me5)]2 or [RhCl(μ-Cl)(η5-C5Me5)]2 instead. Deuterium labelling of CyL1, CyL1, PhL1, and PhL2 enabled the assignment of the methylene protons to be confirmed from 1H NMR spectroscopy. All new compounds have been characterised using a range of spectroscopic and analytical techniques. Single crystal X-ray structures have been determined for CyL1, 1d·3OEt2,1f·2CDCl3·OEt2, 2b, 2c, 2d·CDCl3, 2e·0.5OEt2 and 6b·1.5CDCl3. The free phenolic group in CyL1, 1d·3OEt2,1f·2CDCl3·OEt2, 2b and 2d·CDCl3 participates in intra- or intermolecular O−H···O hydrogen bonding.

Hydrophosphination reactions with transition metal ferrocenylphosphine complexes.

The group 6 metal mono-, bis- and tris-ferrocenylphosphine complexes [M(CO)5(PH2Fc)] (1a, M = Cr; 1b, M = Mo; 1c, M = W), cis-[M(CO)4(PH2Fc)2] (2a, M = Cr; 2b, M = Mo; 2c, M = W) and fac-[M(CO)3(PH2Fc)3] (3a, M = Cr; 3b, M = Mo; 3c, M = W) [Fc = Fe(η(5)-C5H4)(η(5)-C5H5)] were prepared and fully characterised. IR and NMR spectroscopy and single-crystal X-ray diffraction analysis indicate that FcPH2 is as good a σ donor as PhPH2 but is easier to handle and furthermore has a redox-active ferrocenyl group. Complex 1c was employed in the hydrophosphination of acrylonitrile and methyl acrylate in the presence of catalytic amounts of KOtBu giving the secondary phosphine complexes [W(CO)5{PH(Fc)(CH2CH2CN)}] (4a) and [W(CO)5{PH(Fc)(CH2CH2C(O)OMe)}] (4b). In addition, FcP(CH2CH2CN)2 (5) was prepared by a similar method from FcPH2 and acrylonitrile. These hydrophosphination products represent a convenient method for the modification of phosphines.

ChemInform Abstract: Synthesis, Reactivity, and Coordination Chemistry of Secondary Phosphines

AbstractReview: 150 refs.

Using Monovalent Phosphorus Compounds to Form P–C Bonds

User friendly P–C: Electrophilic terminal phosphinidene complexes [RPW(CO)5] react with ArB(OH)2 to give the corresponding secondary phosphine complexes [{R(Ar)PH}W(CO)5]. This method enables the formation of PC bonds through the combination of a wide array of heterocyclic and aryl boronic acids with various electrophilic phosphinidene complexes. The final products incorporate a PH bond that can be used for further transformations.

Primary and Secondary Phosphine Complexes of Iron Porphyrins and Ruthenium Phthalocyanine: Synthesis, Structure, and P−H Bond Functionalization

Reduction of [Fe(III)(Por)Cl] (Por = porphyrinato dianion) with Na2S2O4 followed by reaction with excess PH2Ph, PH2Ad, or PHPh2 afforded [Fe(II)(F20-TPP)(PH2Ph)2] (1a), [Fe(II)(F20-TPP)(PH2Ad)2] (1b), [Fe(II)(F20-TPP)(PHPh2)2] (2a), and [Fe(II)(2,6-Cl2TPP)(PHPh2)2] (2b). Reaction of [Ru(II)(Pc)(DMSO)2] (Pc = phthalocyaninato dianion) with PH2Ph or PHPh2 gave [Ru(II)(Pc)(PH2Ph)2] (3a) and [Ru(II)(Pc)(PHPh2)2] (4). [Ru(II)(Pc)(PH2Ad)2] (3b) and [Ru(II)(Pc)(PH2Bu(t))2] (3c) were isolated by treating a mixture of [Ru(II)(Pc)(DMSO)2] and O=PCl2Ad or PCl2Bu(t) with LiAlH4. Hydrophosphination of CH2=CHR (R = CO2Et, CN) with [Ru(II)(F20-TPP)(PH2Ph)2] or [Ru(II)(F20-TPP)(PHPh2)2] in the presence of (t)BuOK led to the isolation of [Ru(II)(F20-TPP)(P(CH2CH2R)2Ph)2] (R = CO2Et, 5a; CN, 5b) and [Ru(II)(F20-TPP)(P(CH2CH2R)Ph2)2] (R = CO2Et, 6a; CN, 6b). Similar reaction of 3a with CH2=CHCN or MeI gave [Ru(II)(Pc)(P(CH2CH2CN)2Ph)2] (7) or [Ru(II)(Pc)(PMe2Ph)2] (8). The reactions of 4 with CH2=CHR (R = CO2Et, CN, C(O)Me, P(O)(OEt)2, S(O)2Ph), CH2=C(Me)CO2Me, CH(CO2Me)=CHCO2Me, MeI, BnCl, and RBr (R = (n)Bu, CH2=CHCH2, MeC[triple bond]CCH2, HC[triple bond]CCH2) in the presence of (t)BuOK afforded [Ru(II)(Pc)(P(CH2CH2R)Ph2)2] (R = CO2Et, 9a; CN, 9b; C(O)Me, 9c; P(O)(OEt)2, 9d; S(O)2Ph, 9e), [Ru(II)(Pc)(P(CH2CH(Me)CO2Me)Ph2)2] (9f), [Ru(II)(Pc)(P(CH(CO2Me)CH2CO2Me)Ph2)2] (9g), and [Ru(II)(Pc)(PRPh2)2] (R = Me, 10a; Bu(n), 10b; Bn, 10c; CH2CH=CH2, 10d; CH2C[triple bond]CMe, 10e; CH=C=CH2, 10f). X-ray crystal structure determinations revealed Fe-P distances of 2.2597(9) (1a) and 2.309(2) A (2bx 2 CH2Cl2) and Ru-P distances of 2.3707(13) (3b), 2.373(2) (3c), 2.3478(11) (4), and 2.3754(10) A (5b x 2 CH2Cl2). Both the crystal structures of 3b and 4 feature intermolecular C-H...pi interactions, which link the molecules into 3D and 2D networks, respectively.

Water-soluble hydroxyalkylated phosphines: examples of their differing behaviour toward ruthenium and rhodium

The reaction of P(CH2OH)3 (I) and P(C6H5)(CH2OH)2 (II) with RuCl3 in methanol eliminates two equivalents of formaldehyde to yield the mixed tertiary and secondary phosphine complexes all-trans-[RuCl2(P(CH2OH)3)2(P(CH2OH)2H)2] (1) and [RuCl2(P(C6H5)(CH2OH)2)2(P(C6H5)(CH2OH)H)2] (2), respectively. There is a high degree of hydrogen-bonding interactions between the hydroxymethyl groups in 1 and 2, although the phenyl groups of the latter reduce the extent of the network compared to 1. The generation of these mixed secondary and tertiary phosphine complexes is unprecedented. Under the same reaction conditions, the tris(hydroxypropyl)phosphine III formed no ruthenium complex. The reaction of P(CH2OH)3, P(C6H5)(CH2OH)2 and P{(CH2)3OH}3 with [RhCl(1,5-cod)]2 in an aqueous/dichloromethane biphasic medium yielded [RhH2(P(CH2OH)3)4]+ (3), [RhH2(P(C6H5)(CH2OH)2)4]+ (4) and [Rh(P(C6H5)(CH2OH)2)4]+ (5) and [Rh(P{(CH2)3OH}3)4]+ (6), respectively. Treating 5 with dihydrogen rapidly gave 4. The hydroxypropyl compound 6 formed the corresponding dihydride much more slowly in aqueous solution, although [RhH2(P{(CH2)3OH}3)4]+ (7) was readily formed by reaction with dihydrogen. Two separate reaction pathways are therefore involved; for P(CH2OH)3 and to a lesser extent P(C6H5)(CH2OH)2, the hydride source in the product is likely to be the aqueous solvent or the hydroxyl protons, whilst for P{(CH2)3OH}3 an oxidative addition of H2 is favoured. The protic nature of and was illustrated by the H-D exchange observed in d2-water. Dihydrides 3 and 4 reacted with carbon monoxide to yield the dicarbonyl cations [Rh(CO)2(P(CH2OH)3)3]+ (8) and [Rh(CO)2(P(C6H5)(CH2OH)2)3]+ (9). The analogous experiment with [RhH2(P{(CH2)3OH}3)4]+ resulted in phosphine exchange, although our experimental evidence points to the possibility of more than one fluxional process in solution.

Combining phosphinidene units with malonate anion: Synthesis of highly functional phosphine complexes

AbstractMalonate anion traps the [RP‐W(CO)5] bridge of 7‐phosphanorbornadiene complexes 1–3 to give functional secondary phosphine complexes [RP(H)‐CH(CO2Et)2]W(CO)5 (7–9). Metalation of these complexes by NaH in THF occurs at the malonic CH group, but the alkylation of the resulting carbanions preferentially takes place at phosphorus. When R stands for β‐chloroethyl, the corresponding carbanion cyclizes to give the functional phosphirane complex 11. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:258–262, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20014

Highly bulky and electron-rich terminal ruthenium phosphido complexes: new donor ligands for palladium-catalyzed suzuki cross-couplings.

Secondary phosphine complexes of the formula [(eta(5)-C(5)H(5))Ru(L)(2)(PHR(2))](+) BAr(F)(-) are prepared from cationic ruthenium N(2) complexes and PHR(2) (R = Ph (a), t-Bu (b), Cy (c)). Additions of t-BuOK or NaN(SiMe(3))(2) give the phosphido complexes (eta(5)-C(5)H(5))Ru(L)(2)(PR(2)) ((L)(2) = (PEt(3))(2) (5a-c), depe (6a,b)) in high NMR yields. These rapidly oxidize in air to give isolable RuP(=O)R(2) species. Complex 5a is more basic than the rhenium analogue (eta(5)-C(5)H(5))Re(NO)(PPh(3))(PPh(2)), and 6b is more basic than P-t-Bu(3). Complexes 5a-c and 6b are effective ligands for palladium-catalyzed Suzuki reactions. The catalyst from 6b is nearly as reactive as that from the benchmark ligand P-t-Bu(3).

Terminal phosphido-complexes of co-ordinatively saturated and unsaturated platinum(II)

Reactions of [Pt{PPh(CH2CH2PPh2)2}Cl]Cl or [Pt{P(CH2CH2PPh2)3}Cl]Cl with PR2H (R = Ph or C6H11) and TI(O3SCF3) give secondary phosphine complexes [Pt{PPh(CH2CH2PPh2)2}(PR2H)][O3SCF3]2 or [Pt{P(CH2CH2PPh2)3}](PR2H)][O3SCF3]2. The corresponding terminal phosphido complexes were prepared by deprotonation with aqueous KOH or Na[N(SiMe3)2]. The new complexes were characterised by 31P and 195Pt n.m.r. spectroscopy. Phosphorus-31 n.m.r. spectra indicate that the geometry at the terminal phosphido phosphorus is pyramidal.

ChemInform Abstract: Synthesis, Structure, Dynamic Behavior, and Reactivity of Rhenium Phosphido Complexes (η5‐C5H5)Re(NO)(PPh3)(PR2). The “Gauche Effect” in Transition‐Metal Chemistry.

AbstractThe air‐sensitive title complexes (IV) are obtained from the secondary phosphine complexes (III), which in turn are prepared from (I) as shown in the scheme.

Metal complexes of sulphur ligands. Part 22. Reaction of platinum(II) and palladium(II)NN-dialkyldithiocarbamates with diphenylphosphine chalcogenides

Reaction of [Pt(S2CNR2)2](R = Et or Pri) with either Ph2P(O)H or prehydrolysed Ph2PCl in alcohols give high yields of [Pt(S2CNR2){(Ph2PO)2H}](1). In contrast, reaction of [Pt(S2CNR2)2] with Ph2P(S)H in alcohols give a variety of products, depending on the amount of sulphide used, the amount of water present in the reaction mixture, and the duration of reaction. Thus with an excess of Ph2P(S)H in dry methanol, [NR2H2][Pt(S2CNR2)(Ph2PS)2](2) are formed and the structure of (2a)(R = Et) has been verified by X-ray analysis. The crystals are orthorhombic, space group P212121 with a= 21.098(18), b= 11.679(8), c= 14.816(18)A. Prolonged reaction in dry methanol gives [Pt(S2CNR2){Ph2P(OMe)}(Ph2PS)](5) whereas with 1 : 1 mol ratios of Pt : Ph2P(S)H, small amounts of the binuclear [{ Pt(S2CNEt2)(Ph2PS)}2](6a) are formed. These are obtained in much higher yield by reaction of compound (2) with HCl gas in dry CHCl3 and the structure of (6b)(R = Pri) confirmed by X-ray analysis. The crystals are monoclinic, space group P21/c with a= 12.192(7), b= 9.272(6), c= 24.958(15)A, and β= 116.232(28)°. Small amounts of the secondary phosphine complexes [Pt(S2CNR2)(Ph2PH)(Ph2PS)](4) are also formed in all these reactions and these can be synthesised in high yield by direct reaction of compound (2) with Ph2PH. Finally, in wet methanol, the neutral complexes [Pt(S2CNR2)(Ph2POHSPPh2)](3) are formed together with some of compound (2). The corresponding reaction of [Pd(S2CNEt2)2] with an excess of Ph2P(S)H in dry methanol gives [NEt2H2][Pd(S2NEt2)(Ph2PS)2] and [{Pd(S2CNEt2)(Ph2PS)}2] whereas the reaction of [Pt(S2CNR2)2] with Ph2P(Se)H gives only [Pt(S2CNR2)(Ph2PH)(Ph2PSe)] in high yield. All these compounds have been characterised by a variety of physicochemical methods and a reaction scheme to account for the formation of compounds (2)–(6) from reaction of [Pt(S2CNR2)2] with Ph2P(S)H is suggested.