Livio Zanotto

Functionalized ylides: new trends in organometallic chemistry

The coordination and organometallic chemistry of P- and As-carbonyl stabilized ylides is reviewed. As a general feature, the coordination chemistry of R3ECHCOR′-type (E=P, As) ligands appears to be dominated by C(ylide) metal coordination, although a few examples of O(ylide)-bound complexes are known. The factors addressing C(ylide)-vs. O(ylide)-coordination in Pt(II) and Pd(II) systems are examined. The Ni(II) complexes containing P,O-chelate ylide ligands are also discussed, with a special emphasis on their catalytic activity. The synthesis and reactivity of phosphonium functionalized isocyanides and their corresponding ylides, which provide a new route to metal coordinated indole systems, are described. Finally, the reactivity of Ph3PCCO towards metal substrates is summarized including the formation of ketenyl complexes.

Influence of ancillary ligands in the coordination mode of P and As carbonyl stabilized ylides on Pt(II) systems. X-ray structure of trans-[Pt(PPh3)2(CF3) {OC(OCH3)C(H) (PPh3)}] [BF4]·0.5CH2Cl2

Abstract The carbonyl stabilized P and As Ph3PHCOR (RCH3, Ph, OCH3) and Ph3ASCHCOR (RCH3, PH, OCH3) have been reacted with some platinum(II) complexes bearing ancillary ligands with different steric hindrance, in order to determine the factors that influence the C- versus O-coordination mode of the ylides. Thus, the reactions of [(dppe)PtCl2] and [(dppv)PtCl2] with Ph3PCHCOR (R^z.dbnd;CH3, Ph) give the O-coordinated complexes, while with Ph3PCHCOOCH3 they give the corresponding C-coordinated derivatives. The reactions of trans-[PPh3)2(CF3)Pt(solv)]+BF−4 yieldd the O-coordinated compounds and the reactions with [Pt(C3H5)Cl]4 give selectivity the C-coordinated derivatives as well as the reactions with the dimer [ PlCl(P(Bu 2 ) 2 C(Me) 2 C H 2 }] 2 . The derivative trans-[Pt(PPh3)2(CF3){OC(OCH3)=C(H)(PPh3)}][BF4]] crystallizes in the triclinic group P1 (No. 2), a = 10.385(4), b = 14.844(5), c = 18.511(6) →A , α = 96.46(2), β=99.79(2), γ = 97.00(2)°, V = 2765(1) a A 3 , Z = 2 . The values of coordination distances and of the PtOC angle appear influenced by steric factors.

Preparation and characterization of PdIII-ylide complexes of type Pd(CNR)(η3-2-XC3H4)[Ph3PC(H)COMe] BF4 (X = H, Me; R = p-C6H4OMe, C(Me)3, Me, C6H11, p-C6H4NO2). Crystal structure of Pd[CNC(Me)3]-(η3-2-MeC3H4)[Ph3PC(H)COMe] BF4

Seven compounds of general formula Pd(CNR)(η3-2-XC3H4)[PH3PC(H)COMe]BF4(X = H, R = p-C6H4OMe (1, R = C(Me)3 (2; X = Me, R = p-C6H4OMe (3), C(Me)3 (4), Me (5), C6H11 (6), p-C6H4NO2 (7)) have been prepared by chloride abstraction from PdCl(η3-2-XC3H4)[Ph3PC(H)COMe] (X = H, me) with AgBF4 and subsequent reaction of the cationic intermediate with the appropriate isocyanide ligand. all the complexes have been characterized by analytical and spectroscopic (IR, 1H and 31P1H NMR) data. They have been shown to be a mixture of two diastereoisomeric forms arising from the simultaneous presence on the palladium atom of the asymmetric ylidic carbon atom and the η3-allyl ligand. The determination of the crystal structure of complex 4 showed that in the solid state only one diastereoisomer is present. The crystals are monoclinic, space group Pc with a 9.833(3), b 14.383(4), c 11.762(4) A, β 114.68(3)°, and Z = 2. Final full-matrix least-squares refinement, based on 2413 reflections, converged to R = 0.050. The keto-stabilized ylide ligand is C bonded to the metal with a PdC distance of 2.175 (9) A.

Reactivity of carbonyl stabilized ylides with Zeise's salt. Synthesis, characterization of mono- and bis-ylidic Pt(II) derivatives and X-ray crystal structure of the {PtCl2[C(H)COCH3(PPh2-o-C6H4)[PPh3CH2COCH3] complex

Abstract Phosphorus and arsenic keto-stabilized ylides (APPY, CMPPY, BPPY, BCyPY-OMe, APAsY, CMPAsY, BPAsY) react with Zeises salt to give the corresponding monosubstituted Pt(II) complexes trans-[PtCl2(η2-C2H4) (ylide)] (1–7). The bis-ylide complexes trans-[PtCl2(ylide)2] (8–12) and trans-[PtCl2(ylide)(ylide′)] (13–17) can bbe prepared by reaction of 1–7 with the corresponding ylides. Upon heating complex 8 trans-{PtCl2[C(H) (PPh3) COCH3]2} in THF a cyclization reaction occurred to give {PtCl2[C(H)COCH3(PPh2-o-C6H4)]}[Ph3PCH2COCH3] (18). The molecular structure of compound 18 was determined by X-ray diffraction. The molecule consists of a metallic anion and a phosphonium counterion. Compound 18 crystallizes in the monoclinic space group P21/c with unit cell parameters a = 13.855(3), b = 14.242(3), c = 20.173(4) A , β = 109.31(5)°, Z = 4 .

Reactivity of carbon suboxide toward As and P stabilized ylides. Crystal and molecular structure of CH2{C(=O) [C(=AsPh3) (COOMe)]}2

Abstract The reactions of carbon suboxide, C3O2, with a series of stabilized triphenylarsoranes, Ph3As=CHX (X = CN, COOMe, COMe, COPh, COC6H4-p-OMe), yield two different kinds of cmpounds. When X = CN, COOMe the reaction proceeds in a 2:1 ratio (ylide: C3C2) yielding open-chain maloni bis-ylidic compounds (1a,b) whereas in the cases of X = COMe, COPh, COC6H4-p-OME only 1:1 cyclic zwitterionic compounds (2a-c) are obtained. The crystal structure of the bis-ylidic compound 1b has been determined. The crystalas are monoclinic, space group C2/c with a = 19.296(8), b = 10.179(5), c = 19.743(8) A , β = 97.3(1)°, Z = 4 . The molecular parameters are consistent with an important contribution of the dipolar form −OC=CAs+. Carbon suboxide has been reactde also with Ph3P=CHX (X = COC6H4-p-OMe, COOMe) giving the cyclic zwitterionic compounds 3 when X = COC6H4-p-OME, whereas when X = COOMe a mixture of products has been obtained.

Synthesis of heterocyclic systems by activation of isocyanide, carbonyl, trifluoromethyl and nitrile ligands in platinum(II) and palladium(II) complexes

Abstract Pd(II)- and Pt(II)-coordinated isocyanide, carbonyl and trifluoromethyl ligands are converted to heterocyclic carbenes (type I–III structures), while nitrile ligands are converted to oxazolines (type IV/structure) using different synthetic strategies. Thus, RNC ligands in Pt(II) complexes react with HOCH2CH2X/base (XCl, Br; base=nBuLi) to afford five-membered cyclic aminooxycarbenes of the general formula Pt= CN(R)CH 2 CH 2 O (R=alkyl, aryl) (type I structure). The corresponding reactions with Pd(II) isocyanides lead to Pd(O) species. Similar reactions of Pd(II)- and Pt(II)-metal bound isocyanides with NH2CH2CH2Br lead to five-membered cyclic diaminocarbenes of the general formula M CN(R)CH 2 CH 2 N(H) (type I structure). Cyclic five-membered diamino-, aminothio- and aminooxycarbenes of the general type M CN(R)CH 2 CH 2 X (XNH, S, O) (type I structure) are obtained from metal coordinated RNC ligands by reaction with the three-membered heterocycles YCH 2 CH 2 (YNH, aziridine; S, thiirane; O, oxirane), respectively. Among the four-membered heterocycles YCH 2 CH 2 CH 2 (YNH, S, O) only azetidine was found to react with some Pd(II)- and Pt(II)-isocyanides to afford acyclic diaminocarbenes. Pt(II)-coordinated phosphonium-functionalized isocyanides of the type o-(BF4,−R3P+-CH2)C6H4NC (R=alkyl, aryl) react with NEt3 to give indole derivatives (type II structure). When R is a benzyl group, the reaction with KOH produces heterometallacycles (type III structure). Pt(II)-bound CO ligands are converted to cyclic aminooxycarbenes of the type Pt COCH 2 CH 2 N (H) (type I structure). The CF bonds α to Pt in trans-L2PtX(CF3) (XH, LPPh3; XCl, LPMe22Ph) are susceptible to electrophilic attack. The reaction with HBF4, leads to the formation of the highly reactive difluorocarbene intermediate PtCF2+, which reacts with diols and thiols to give five- and six-membered heterocycles of the type Pt CX(CH 2 ) n X (n=2, XO, S; n=3, XO) (type I structure). Nitrile ligands coordinated to Pt(II) in complexes of the type cis- and trans-Cl2Pt(NCR)2 react with HOCH2CH2Cl/base or oxirane/Cl- to afford N-coordinated oxazolines Pt NC(R)OCH 2 CH 2 (type IV structure). Mechanistic and structural aspects as well as some significant reactions and electrochemical behaviour of the metal-coordinated heterocycles are reported.

Solution behaviour and relative stability of the complexes [MCl2(RNCHCHNR)] and [MCl2(py-2-CHNR)] (M=Pd, Pt;R=C6H4OMe-p)

Abstract Even though the α-diimino complexes [MCl 2 (RNCHCHNR)] and [MCl 2 (py-2-CHNR)] (M=Pd, Pt;R=C 6 H 4 OMe- p ) are poorly soluble in chlorinated solvents, such as chloroform and 1,2-dichloroethane, or in acetonitrile, the electronic and 1 H NMR spectra indicate that these compounds are generally present as undissociate monomers with σ, σ′- N,N′ chelate N-ligands in dilute solutions. Only for [PdCl 2 (RNCHCHNR)], some dissociation of the α-diimine occurs in acetonitrile. In dimethylsulfoxide, where the solubility is much higher, no dissociation is observed for the pyridine-2-carbaldimine complexes [MCl 2 (py-2-CHNR)], whereas the 1,2-bis(imino) ethane derivatives [MCl 2 (RNCHCHNR)] are extensively dissociated through a step-wise process involving intermediates with a σ- N monodentate α-diimino group. As is shown by the course of substitution reactions with 2,2′-bipyridine, the higher stability of [MCl 2 (py-2-CHNR)] in dimethylsulfoxide is mainly due to thermodynamic factors (ground state stabilization for the presence of stronger MN bonds) rather than by kinetic factors (higher activation energy for steric strain in the activation states or transients).

Reaction of ketenylidenetriphenylphosphorane, Ph3PCCO, with water: formation of methyltriphenylphosphonium hydrogencarbonate

Abstract The reaction of the oxocumulene ylide ketenylidenetriphenylphosphorane, Ph3PCCO (1), with an excess of water in THF yields a white microcrystalline solid, methyltriphenylphosphonium hydrogencarbonate, which contains one molecule of crystallization water, [Ph3MeP]CO3H·H2O (2). Compound 2 was characterized by IR, multinuclear NMR and ESI mass spectra. The chemical constitution was confirmed by X-ray crystal analysis. On heating, compound 2 decomposes giving CO2, H2O, C6H6 and Ph2MePO.

Reactivity of keteylidenetriphenylphosphorane (Ph3PCCO) with Pt(II) complexes. Evidences of formation of an up to now unknown bis-η1-ketenyl derivative

Abstract Ketenylidenetriphenylphosphorane, Ph 3 PCCO, 1 , has been used to synthesize some Pt(II) η 1 -ketenyl derivatives, through reactions with dimeric and tetrameric chlorine-bridged compounds. Particularly it has been possible to isolate and characterize [Pt(η 3 -C 3 H 5 )Cl{η 1 -C(PPh 3 )CO}], 2 , and [PtCl 2 {η 1 -C(PPh 3 )CO}(PPh 3 )], 3 . Moreover, the reaction of 2 with a further equivalent of 1 , in the presence of AgBF 4 , lead to the formation of [Pt(η 3 -C 3 H 5 ){η 1 -C(PPh 3 )CO} 2 ], 4 , the first bis-η 1 -ketenyl derivative. Compound 4 is stable in solution only at low temperatures and its formation has been inferred unequivocally by IR, 1 H and 31 P-NMR measurements carried out at −50°C.

Carbonyl-stabilized phosphonium ylides as ligands. Equilibrium studies on the reversible formation of PdCl(η3-allyl)(ylide) species

Abstract An UVIR study of the equilibrium between [PdCl(η 3 -2-MeC 3 H 4 )] 2 and the carbonyl-stabilized phosphonium ylides R′ 3 PCHCOR″ in CH 2 Cl 2 at 25 °C reveals that the nucleophilic ability of the ylide to bind to palladium in the PdC(ylide) bonded product [PdCl(η 3 -2-MeC 3 H 4 )(R′ 3 PCHCOR″)] increases with increasing basicity of the ylide towards the proton with steric hindrance by phosphonium substituents playing an adverse role.