Tetrahedron report number 163

It has been established that dihalodiphosphinenickel(II) complexes exhibit extremely high catalytic activity for selective cross-coupling of Grignard reagents with aryl and alkenyl halides. This catalytic reaction can be employed in synthetic practice for reasons of simple procedures, mild reaction conditions, high yields and high purity of the coupling products, and the wide applicability to reactions involving primary and secondary alkyl (regardless of the presence or absence of β-hydrogen (s)), aryl, and alkenyl Grignard reagents and nonfused, fused, and substituted aromatic halides and haloolefins. Limitations lie in sluggish reactions between alkyl Grignard reagents and dihaloethylenes. The most effective catalysts are [Ni{(C6H5)2P(CH2)3P(C6H5)2}Cl2] for alkyl and simple aryl Grignard reagents, [Ni{(CH3)2P(CH2)2P(CH3)2}Cl2] for alkenyl and allylic Grignard reagents and [Ni{P(C6H5)3}2-Cl2] for sterically hindered aryl Grignard reagents and halides. Great stabilizing effects of phosphine ligands on the...

Nickel-phosphine complex-catalyzed Grignard coupling. I. Cross-coupling of alkyl, aryl, and alkenyl Grignard reagents with aryl and alkenyl halides: General scope and limitations.

Catalytic Silylation of Unactivated C-H Bonds.

ion upon treatment with B(C6F5)3 in THF to generate the cationic species [(MAC)Y(CH2SiMe3)][B(C6F5)3(CH2SiMe3)]. However, this salt was found to be highly unstable and could not be isolated as a pure material.97 Fryzuk et al. have developed a remarkable organoyttrium chemistry around the phosphorus-containing macrocycle syn-{P2N2} ({P2N2} ) [PhP(CH2SiMe2NSiMe2CH2)2PPh]). The starting material was the chloride-bridged dimer [{P2N2}Y(μ-Cl)]2, which can be prepared in 95% yield by the reaction of synLi2(THF){P2N2} with YCl3(THF)3 in THF solution. Straightforward metathesis using the very bulky alkyllithium reagent LiCH(SiMe3)2 according to eq 29 (methyl groups on Si omitted for clarity) afforded the monomeric yttrium alkyl species {P2N2}YCH(SiMe3)2 in 92% yield. Use of the less sterically hindered alkyl moiety CH2SiMe3 followed by addition of THF resulted in formation of the THF adduct {P2N2}YCH2SiMe3(THF), whereas the THF-free compound could only be isolated as a highly reactive oily material.98 A quite remarkable samarium alkyl complex of complicated molecular structure was reported by Gambarotta et al.99 Samarium diiodide acted as reducing agent in the reaction with (phenylenebis(3,5-tBu4-salicylidene)iminato)sodium, (3,5tBu4salophen)Na2(THF)3, to give dimeric [Sm2(SBSB)(THF)3]‚2toluene (SB-SB ) C-C bonded 3,5tBu4salophen dimer). The new ligand resulted from the reductive coupling of two imino functional groups of two 3,5-tBu4salophenSm units. Subsequent treatment with MeLi resulted in a novel oxo-bridged dimer (24), featuring alkylation of both samarium atoms and arising from cleavage of the C-C bond connecting the two units, as well as complete reduction of the imine groups of the salophen ligands and THF deoxygenation. In the formula drawing depicted here the bridging phenylene rings are omitted for clarity.99 Carbene complexes of the lanthanide elements have first become available through the use of the stable Arduengo-type carbenes.100,101 Organolanthanide derivatives are readily accessible by adding the heterocyclic carbene ligands to various diand trivalent rare earth complexes such as decamethylsamarocene. Cyclopentadienyl-free derivatives have been obtained by reacting 1,3,4,5-tetramethylimidazol-2-ylidene with the tris(2,2,6,6-tetramethylheptane-3,5-dionato) complexes of yttrium and europium, Ln(THD)3 (Ln ) Y, Eu). The two carbene complexes 25 were isolated as white solids in quantitative yield. The europium complex was structurally characterized by X-ray analysis. Despite the differences in the ionic radii of the two metals 7-coordinate monocarbene adducts are formed in both cases. With 266.3(4) pm the Eu-C distance in (1,3,4,5-tetramethylimidazol-2-ylidene)Eu(THD)3 is comparable to Pr(III)-C and Sm(III)-C distances reported for some isonitrile complexes.102,103 In the 13C NMR spectrum of the yttrium complex the resonance for the former carbene carbon is at δ 199.38 (cf. δ 214 for the free carbene ligand) and shows a 13C-89Y coupling of 33 Hz which indicates that the Y-C bond does not dissociate rapidly on the NMR time scale.101 The bulkier 1,3-diisopropyl-4,5dimethylimidazol-2-ylidene (iPr-Carb) has been used to synthesize a mixed carbene-THF alkyl Lu(CH2SiMe3)3(THF)(Pr-Carb) (26).22d Due to its higher steric demand, the carbene ligand occupies an equatorial position (Lu-C(Carb) ) 249 pm). Somewhat related to the carbene complexes is a highly unusual monomeric samarium bis(iminophosphoranyl) chelate complex which has been reported by Cavell et al.104 Addition of H2C(Ph2PdNSiMe3)2 to a toluene solution of samarium tris(dicyclohexylamide) afforded bright yellow [κ-C,N,N′-C(Ph2Pd NSiMe3)2]Sm(NCy2)(THF) (27). The core of the molecule consists of two nearly planar, fused fourmembered rings with a Sm-C shared edge. With 246.7(4) pm the Sm-C bond length is considerably shorter (10%) than the average samarium-carbon distances, indicating that 27 can be formulated as a carbene complex. Non-Cyclopentadienyl Organolanthanide Complexes Chemical Reviews, 2002, Vol. 102, No. 6 1865

Synthesis and structural chemistry of non-cyclopentadienyl organolanthanide complexes.

A series of unprecedented organoiron complexes of the formal oxidation states −2, 0, +1, +2, and +3 is presented, which are largely devoid of stabilizing ligands and, in part, also electronically unsaturated (14-, 16-, 17- and 18-electron counts). Specifically, it is shown that nucleophiles unable to undergo β-hydride elimination, such as MeLi, PhLi, or PhMgBr, rapidly reduce Fe(3+) to Fe(2+) and then exhaustively alkylate the metal center. The resulting homoleptic organoferrate complexes [(Me4Fe)(MeLi)][Li(OEt2)]2 (3) and [Ph4Fe][Li(Et2O)2][Li(1,4-dioxane)] (5) could be characterized by X-ray crystal structure analysis. However, these exceptionally sensitive compounds turned out to be only moderately nucleophilic, transferring their organic ligands to activated electrophiles only, while being unable to alkylate (hetero)aryl halides unless they are very electron deficient. In striking contrast, Grignard reagents bearing alkyl residues amenable to β-hydride elimination reduce FeXn (n = 2, 3) to clusters of...

Preparation, Structure, and Reactivity of Nonstabilized Organoiron Compounds. Implications for Iron-Catalyzed Cross Coupling Reactions

Metal .sigma.-hydrocarbyls, MRn. Stoichiometry, structures, stabilities, and thermal decomposition pathways

The complexes (Me3M′CH2)3M·2THF (M = Sc or Y; M′= C or Si) and (o-MeOC6H4SiMe2CH2)3Sc have been isolated from the reaction of the appropriate lithium reagent with MCI3 or MCI·nTHF.

Stable silylmethyl and neopentyl complexes of scandium(III) and yttrium(III)

Bridged hydrocarbyl or hydrocarbon binuclear transition metal complexes: classification, structures, and chemistry

The reaction of [(η-C5H5)2MMe2AlMe2](M = Y, Dy, Ho, Er, Tm, or Yb) and pyridine in equimolar amounts gives a series of complexes [{M(η-C5H5)2Me}2] assigned a dimeric structure on the basis of 1H and 13C n.m.r. (M = Y) and i.r. data, and by crystal and molecular structural determinations of [{M(η-C5H5)2Me}2](M = Y or Yb). A similar reaction of [(η-C5H5)2ScMe2AlMe2] with a Lewis base L gives [Sc(η-C5H5)2Me(L)](L = pyridine or tetrahydrofuran). Other reactions described are of [{Y(η-C5H5)2Me}2] with Lewis bases (an amine, phosphine, or phosphine oxide) or with a Lewis acid [Al2MenCl6 –n](n= 2, 4, or 6). A single-crystal X-ray analysis of the isostructural [{M(η-C5H5)2Me}2] has been carried out to R 0.048 (Y) or 0.066 (Yb) and R′ 0.055 (Y) or 0.061 (Yb); the complexes have an approximately tetrahedral metal environment (space group P21/n) with the YMe2Y unit in the yttrium complex remarkably similar to AlMe2Al in [Al2Me6]. Important average bond lengths (A) and angles for the yttrium complex (Yb in parentheses) are: Y–C (cyclopentadienyl) 2.655(18)[2.613(13)] and Y–Me 2.545(11)[2.511(35)]; Y–C–Y 87.7(3)[86.6(3)] and Me–Y–Me 92.3(3)[93.4(4)].

Alkyl-bridged complexes of the d- and f-block elements. Part 2. Bis[bis(η-cyclopentadienyl)methylmetal(III)] complexes, and the crystal and molecular structure of the yttrium and ytterbium species

The neutral [M(CH2SiMe3)3(thf)2](M = Tb, Er, or Yb; thf = tetrahydrofuran) and the ionic [Li(L)4]-[MR4][R = Me3SiCH2; when M = Y, Er, or Yb, L2= Me2NCH2CH2NMe2(tmed); when M = Y, L = thf], [Li(thf)4][M(Cl)R3][M = Er or Yb, R =(Me3Si)2CH], and [LiL2][M(η-C5H4SiMe3)2Cl2][L = 0·5 tmed or thf) are reported; their structures are deduced from i.r. and 13C and 1H n.m.r. (M = Y) spectra, conductivity, and in the case of [Li(thf)4][Yb{CH(SiMe3)2}3Cl], by a single crystal X-ray analysis [l(Yb–C)(av.)= 2·38 A].

Neutral and anionic silylmethyl complexes of the Group 3a and lanthanoid metals; the X-ray crystal and molecular structure of [Li(thf)4][Yb{CH(SiMe3)2}3Cl](thf = tetrahydrofuran)

Ronald Pearce

Papers

Metal .sigma.-hydrocarbyls, MRn. Stoichiometry, structures, stabilities, and thermal decomposition pathways

Stable silylmethyl and neopentyl complexes of scandium(III) and yttrium(III)

Bridged hydrocarbyl or hydrocarbon binuclear transition metal complexes: classification, structures, and chemistry

Alkyl-bridged complexes of the d- and f-block elements. Part 2. Bis[bis(η-cyclopentadienyl)methylmetal(III)] complexes, and the crystal and molecular structure of the yttrium and ytterbium species

Neutral and anionic silylmethyl complexes of the Group 3a and lanthanoid metals; the X-ray crystal and molecular structure of [Li(thf)4][Yb{CH(SiMe3)2}3Cl](thf = tetrahydrofuran)