M. Pilar Gamasa

Recent Developments in the Reactivity of Allenylidene and Cumulenylidene Complexes

Allenylidene and higher cumulenylidene complexes [M]=C(=C)n=CR1R2 (n = 1, 2, 3) have continuously gained significance in the context of transition metal carbene chemistry. Important developments which have been disclosed during the last two years are reviewed. These include a variety of stoichiometric and catalytic reactions of allenylidene complexes and their utility in organic synthesis. The related chemistry of butatrienylidene (n = 2) and pentatetraenylidene (n = 3) complexes as well as theoretical studies are also reviewed.

Indenyl complexes of Group 8 metals

Abstract The present review article is concerned with the state of the art of the chemistry of indenyl Group 8 metal complexes which has undergone significant progress during the last decade. It deals mainly with complexes of the types: (a) bis(indenyl) sandwich compounds [M(η5-C9H7−xRx)2] (R=H, Me); (b) half-sandwich derivatives [M(η5-C9H7−xRx)(CO)2]2 and [M(η5-C9H7−xRx)XL2] (X=halides, H, alkyl, acetylide; L=two electron donor ligands); (c) cationic complexes [M(η5-C9H7−xRx)L2L′]+ (L, L′=two electron donor ligands). A detailed account of the synthesis, structural and reactivity aspects is presented including kinetic studies and catalytic processes. A discussion of the structural features and coordination modes of the indenyl group with special attention to its distortion parameters is presented. The reactivity studies include redox (chemical and electrochemical) processes, insertion reactions, ring transformations as well as ligand exchange processes in half-sandwich derivatives [M(η5-C9H7−xRx) XL2]. In particular, a detailed discussion of the ability of the moiety [M(η5-C9H7−xRx)L2] to stabilize unsaturated carbene groups such as vinylidene (CCR2, allenylidene CCCR2 and α,β-unsaturated alkenyl carbene C(H)C(R1)CRR′ complexes is presented. The influence of the indenyl ring on the regio- and stereoselective nucleophilic additions to these carbene groups allows selective synthesis leading to either allenyl or functionalized alkynyl complexes. A large number of the latter have been synthesized some of them showing excellent non-linear optical properties.

Synthesis and characterization of novel σ-alkynyl cyclopentadienyl iron(II) complexes [Fe(CCR)L2(η-C5H5)] [L CO; L2 bis(diphenylphosphino)methane (dppm)]. Crystal structure of [Fe(CCC6H5)(dppm)(η-C5H5)]

Abstract The synthesis of novel σ-alkynyl cyclopentadienyl iron(II) complexes of the type [Fe(CCR)L 2 (η-C 5 H 5 )] [L  CO; R  SiMe 3 , t Bu, CO 2 Me; L 2 = bis(diphenylphosphino)methane (dppm), R  SiMe 3 , t Bu, CCO 2 Me, H, C 6 H 5 ] is described. IR and 1 , 31 P{ 1 H} and 13 C NMR data are discussed. The structure of [Fe(CCPh)(dppm)(η-C 5 H 5 )] has been determined by an X-ray diffraction study. the coordination around the Fe atom of the cyclopentadienyl ring (considered as bonded at its centroid), the two P atoms of the dppm molecule acting as a chelating ligand, and the terminal carbon of the phenylacetylide ligand, can be described as a three-legged piano stool. The stabilities of the dppm chelate rings in the complexes have been studied, and their reactions with CO under atmospheric or higher pressure examined.

Synthesis and crystal structure of [Cu3(μ3-η1-CCPh)(μ-dppm)3][BF4]2, a tricopper(I) complex containing a μ3-η1 acetylide group and three bis(diphenylphosphino)methane (dppm) bridging ligands

Abstract The synthesis of the cationic trinuclear copper(I) complex [Cu 3 (CCPh)(dppm) 3 ][BF 4 ] 2 is described. An X-ray structure determination shows a triangular array of copper atoms with three diphosphine ligands Ph 2 PCH 2 PPh 2 (dppm) bridging each edge of the triangle and a μ 3 -η 1 phenyl acetylide group bound to the Cu 3 unit.

Reactions of novel cationic diphenylallenylidene complexes [Ru(CC CPh2)L2(η-C9H7)]+(L = PPh3; L2= bis(diphenylphosphino)methane, dppm or 1,2-bis(diphenylphosphino)ethane, dppe) with neutral and anionic nucleophiles

Abstract The synthesis of novel allenylideneruthenium(II) complexes [Ru(CCCPh 2 )L 2 (η-C 9 H 7 )] [PF 6 ] [L = PPh 3 ; L 2 = bis(diphenyl phosphino)methane (dppm) or 1,2-bis(diphenylphosphino)ethane (dppe)] is described. The allenylidene complexes are unreactive towards methanol but other nucleophiles [PMe 3 , NaOMe, LiCCR (R = Ph, n-C 3 H 7 )] can be added regioselectively to the C γ atom to give alkynyl derivatives. [Ru{CCCPh 2 (PMe 3 )}(dppm)(η-C 9 H 7 )] [PF 6 ] isomerizes in tetrahydrofuran solution to the thermodynamically stable product [Ru{C(PMe 3 )CCPh 2 }(dppm)(η-C 9 H 7 )] [PF 6 ].

Dimerization of terminal alkynes catalyzed by indenyl ruthenium(II) complexes

Abstract The indenyl ruthenium complexes [Ru(η 5 -C 9 H 7 )X(dppm)] (X=H, 1 ; CCPh, 2 ; ( E )-CHCHPh, 3 ), [Ru(η 5 -C 9 H 7 )X(PPh 3 ) 2 ] (X=H, 4 ; CCPh, 5 ), [Ru(η 5 -C 9 H 7 )X(dppe)] (X=H, 6 ; CCPh, 7 ), [Ru(η 5 -C 9 H 7 )Cl(COD)] ( 8 ), (dppm=bis(diphenylphosphino)methane; dppe=1,2-bis(diphenylphosphino)ethane; COD=1,5-cyclooctadiene) catalyze the dimerization of phenylacetylene to ( E )- and ( Z )-1,4-diphenylbut-1-en-3-yne. The cyclopentadienyl complex [Ru(η 5 -C 5 H 5 )H(dppm)] ( 9 ) is inactive. The activity of the complexes depending on phosphine follows the order dppm>bis-PPh 3 >dppe, after 13 h. The catalysis is less efficient for the aliphatic 1-octyne than for phenylacetylene. Addition of PPh 3 to complexes 5 and 8 enhances the conversion to the dimerization products. The isomeric distribution of E and Z enynes is dependent on different factors, such as temperature, reaction time, substrate to catalyst molar ratio, nature of σ-ligand. The isomers ( E ) and ( Z )-1,4-diphenylbut-1-en-3-yne are synthesized on a semipreparative scale by catalysis of either complex 4 or 5 , and can be separated from the isomeric mixture by standard methods. The procedure represents a one pot preparation of the two isomers starting from one terminal alkyne by CH activation.

Copper(I) complexes containing 1,1′-bis(diphenylphosphino) ferrocene (dppf) as a chelate ligand. X-ray crystal structures of [Cu2(μ-Cl)2(κ2-P,P-dppf)2] and [Cu(CNtBu)2(κ2-P,P-dppf)][BF4]

Abstract Copper(I) complexes [Cu(CNR)2(κ2-P,P-dppf)][BF4] (R=tBu (1), 2,6-Me2C6H3 (2), Cy (3), Bz (4)) containing the chelating dppf ligand (dppf=1,1′-bis(diphenylphosphino)ferrocene) have been prepared by reaction of the complex [Cu2(μ-Cl)2(κ2-P,P-dppf)2] with the corresponding isocyanide CNR (molar ratio 1:1). Alternatively, complexes 1–4 can also be obtained by the reaction of the acetonitrile complexes [Cu(MeCN)2(κ2-P,P-dppf)][BF4] with 2.5 equivalents of CNR in refluxing dichloromethane. The crystal structures of [Cu2(μ-Cl)2(κ2-P,P-dppf)2] and [Cu(CNtBu)2(κ2-P,P-dppf)][BF4], determined by X-ray diffraction, are also reported.

Synthesis, Structural Characterisation and Electrochemical Studies of Neutral Alkenylcarbyne Tungsten Complexes Bearing Chelating Bidentate and Tridentate Phosphanes

Neutral alkenylcarbyne complexes [X = SCN; n = 1 (2a), 4 (2b). X = OCN; n = 1 (2c), 4 (2d)] were prepared by reaction of the acetonitrile complexes [n = 1 (1a), 4 (1b)] with M[OCN] or M[SCN] (M = Na, K, Bu4N), and were fully characterised. The synthesis of complex 3, containing the tridentate phosphane triphos [triphos = PPh(CH2CH2PPh2)2], is also described. The structures of 2b and 3 were determined by X-ray diffraction methods. In both complexes, the coordination of the W atom was octahedral, with the N-bonded thiocyanate (2b) or the chlorine (3) anions trans to the alkenylcarbyne group. The W−N and W−Cl bond lengths were significant longer than the average found in the literature; this indicates the remarkable trans influence of the alkenylcarbyne moiety. The electrochemical behaviour of complexes 2a−d and 3, as well as that of the related compounds D (2e: X = F, n = 4), (2f: X = Cl, n = 1), (2g: X = S2P(OEt)2, n = 1) and A (4: n = 1) was investigated by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic media and at a Pt electrode. They underwent irreversible anodic and cathodic processes, the former usually being multi-electronic in the time scale of CPE and involving anodically induced proton dissociation from the alkenylcarbynes. These ligands behave as remarkably strong π-electron acceptors and from the linear relationship between the oxidation potential of the first anodic wave and the electrochemical PL ligand parameter, it was possible to estimate, for the first time for a carbyne-containing metal centre, that is, the site {(dppe)(CO)2W≡C−R}, the values of the electrochemical electron richness (Es) and the polarisability (β) parameters. These values indicate that this site has low electron richness and low polarisability; this is accounted for by the extensive π-electron acceptance of the alkenylcarbyne ligand. PL was also estimated for the S2P(OEt)2− ligand, which was shown to act as a rather strong net electron releaser.

Synthesis and characterization of 2-oxacycloalkylideneruthenium(II) complexes: X-ray crystal structure of the 2-oxacycloheptylidene complex [Ru{=COCH2(CH2)3CH2}(η5-C9H7)(PPh3)2][PF6].CH2Cl2

Abstract The oxacyclocarbene complexes [Ru{ COCH 2 (CH 2 ) n C H2}(η5-C9H7)LL′][PF6]·(L=L′=PPh3, n=1 (2a), 2 (3a), 3 (5a); L=L′=PMe2Ph, n=1 (2b), 2 (3b), 3 (5b); LL′=dppm, n=1 (2c), 2 (3c), 3 (5c); L=PPh3, L′=PMe3, n=1 (2d), 2 (3d), 3 (5d)) have been prepared by reaction of [RuCl(η5-C9H7)LL′] with 3-butyn-1-ol, 4-pentyn-1-ol and 5-hexyn-1-ol in refluxing ethanol and in the presence of NaPF6. The process involves alkyne to vinylidene tautomerization to give hydroxyalkylvinylidene intermediate complexes. The vinylidene complexes [Ru{CC(H)(CH2)3CH2OH}(η5-C9H7)LL′][PF6] (L=L′=PPh3 (4a), L=L′=PMe2Ph (4b), L=PPh3, L′=PMe3 (4d)) have been isolated from the reaction of [RuCl(η5-C9H7)LL′] with 5-hexyn-1-ol. The first structure for a 2-oxacycloheptylidene complex, 5a, has been determined by X-ray diffraction methods. The molecular structure shows the typical pseudooctahedral three-legged piano-stool geometry around the ruthenium atom, which is linked to the phosphorus atoms of the triphenylphosphine ligands and to the Cα of the oxacyclic carbene ligand; the coordination around the ruthenium atom is completed by a η5-bonded indenyl ligand with the benzo ring orientated nearly trans to the carbene group (CA=16.6(6)°). The RuC1 distance, 1.89(1) A, is somewhat shorter than that found for other oxacyclic carbene ruthenium(II) complexes. The oxacycloheptylidene ring adopts a ‘pseudochair’ conformation for the seven member ring and shows an appreciable deviation from vertical orientation (DA=29.7(5)°).

Synthesis of indenyl-ruthenium(II) σ-alkynyl complexes via nucleophilic addition of (1R)-(+)- and (1S)-(−)-camphor enolates on the allenylidene group of [Ru(CCCPh2)(η5-C9H7)(PPh3)2][PF6]: Efficient synthesis of novel optically pure vinylidene derivatives

Abstract The diphenylallenylidene complex [Ru(CCCPh 2 )(η 5 -C 9 H 7 )(PPh 3 ) 2 ][PF 6 ] ( 1 ) regioselectively reacts at the C γ atom with the lithium enolate derived from (1 R )-(+)-camphor to yield σ-alkynyl derivative [Ru{CCCPh 2 (C 10 H 15 O)}(η 5 -C 9 H 7 )(PPh 3 ) 2 ] ( 2 ). Complex 2 was obtained as a non-separable mixture of two diastereoisomers, i.e. (1 R ,3 S ,4 R )- 2 and (1 R ,3 R ,4 R )- 2 (ca. 3:2 ratio), in which the alkynyl fragment is located in exo or endo disposition on the camphor skeleton, respectively. Protonation of this mixture with HBF 4 ·Et 2 O affords the vinylidene derivative [Ru{CC(H)CPh 2 (C 10 H 15 O)}(η 5 -C 9 H 7 )(PPh 3 ) 2 ][BF 4 ] ( 3 ) as a single diastereoisomer, i.e. (1 R ,3 S ,4 R )- 3 , showing an exo disposition of the vinylidene group. The structure of complex (1 R ,3 S ,4 R )- 3 has been confirmed by X-ray diffraction. The molecular structure shows the typical pseudo-octahedral three-legged piano-stool geometry around the ruthenium atom, which is linked to the phosphorus atoms of the PPh 3 ligands, to the η 5 -bonded indenyl ligand, and to an almost linear vinylidene chain (RuC(1)C(2)=165.6 (18)°) with a RuC(1) bond length of 1.88 (2) A. Demetalation of (1 R ,3 S ,4 R )- 3 , by treatment with acetonitrile at reflux, yields the terminal alkyne HCCCPh 2 (C 10 H 15 O) ( 4 ) and the nitrile complex [Ru(NCMe)(η 5 -C 9 H 7 )(PPh 3 ) 2 ][BF 4 ] ( 5 ). Compound 4 was obtained as a non-separable mixture of two diastereoisomers, i.e. (1 R ,3 S ,4 R )- 4 and (1 R ,3 R ,4 R )- 4 (ca. 3:1 ratio). Related reactions starting from diphenylallenylidene 1 and the (1 S )-(−)-camphor enolate are also reported.