Philip J. Harford

Deprotonative Metalation of Chloro‐ and Bromopyridines Using Amido‐Based Bimetallic Species and Regioselectivity‐Computed CH Acidity Relationships

A series of chloro- and bromopyridines have been deprotometalated by using a range of 2,2,6,6-tetramethylpiperidino-based mixed lithium-metal combinations. Whereas lithium-zinc and lithium-cadmium bases afforded different mono- and diiodides after subsequent interception with iodine, complete regioselectivities were observed with the corresponding lithium-copper combination, as demonstrated by subsequent trapping with benzoyl chlorides. The obtained selectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase and as a solution in THF by using the DFT B3LYP method.

Amidocuprates for Directed ortho Cupration: Structural Study, Mechanistic Investigation, and Chemical Requirements†

Organocuprate(I) complexes are immensely valuable reagents for both industrial and research chemistry. During the past few decades, heteroleptic organocuprates bearing alkynyl, cyano, phenylthio, and phosphino groups have secured an important place in organic synthesis. Organo-amidocuprates also represent an important class of heteroleptic cuprates in organic transformations, especially in stereoselective syntheses. In this context, we have recently proposed new uses for amidocuprates, TMPCu-ates ([RCu(TMP)(CN)Li]; R = alkyl, phenyl, and TMP; TMP = 2,2,6,6-tetramethylpiperidido), which promote the highly chemoselective, directed ortho cupration of multifunctionalized aromatic compounds under mild conditions. The aryl cuprate intermediate can be employed not only in the trapping of electrophlies, but also in oxidative ligand coupling to form new C C bonds with alkyl/aryl groups or to introduce a hydroxy group (Scheme 1). Organocuprate(I) chemistry is dominated by two structure types: the Gilman-type and the Lipshutz-type. The basic diorganocuprate(I) unit in each adopts a linear [R-CuR] arrangement. Gilman-type species are known to exhibit homodimeric structures (Scheme 2a). Theoretical predictions of a preference for head-to-tail dimerization of heteroleptic cuprates have been confirmed by the structure of [MesCu(NBn2)Li] (Mes = mesityl, Bn = benzyl), [9]

Structural Effects in Lithiocuprate Chemistry: The Elucidation of Reactive Pentametallic Complexes

TMPLi (TMP=2,2,6,6-tetramethylpiperidide) reacts with CuI salts in the presence of Et2O to give the dimers [{(TMP)2Cu(X)Li2(OEt2)}2] (X=CN, halide). In contrast, the use of DMPLi (DMP=cis-2,6-dimethylpiperidide) gives an unprecedented structural motif; [{(DMP)2CuLi(OEt2)}2LiX] (X=halide). This formulation suggests a hitherto unexplored route to the in situ formation of Gilman-type bases that are of proven reactivity in directed ortho cupration.

Towards the Synthesis of Guanidinate- and Amidinate-Bridged Dimers of Mn and Ni

Reactions of Cp2M (Cp = cyclopentadienyl, M = Mn, Ni) with lithium amidinates and guanidinates are reported. The highly oxophilic nature of Mn leads to the isolation of the interstitial oxide Mn4O(MeN···CH···NMe)6 (4) in preference to the intended paddle-wheel homodimer Mn2(MeN···CH···NMe)4 when employing the sterically uncongested amidinate [MeN···CH···NMe]– ligand. In contrast, an analogous reaction using Cp2Ni yielded Ni2(MeN···CH···NMe)4 (5). The use of monoprotic guanidinate ligands also gave contrasting results for Mn and Ni. In the first case, the highly unusual spirocycle Mn{μ-NC(NMe2)2}4Li2·3THF (6) was produced in low yield. For M = Ni, use of the [hpp]– (1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) ligand gives results comparable with the synthesis of 5, with Ni2(hpp)4 (7) isolated. In contrast to recent data obtained using Cp2Cr, the guanidinate ligands do not sequester coformed CpLi. Density functional theory analysis corroborates the view that the intermetal distance in each of the reported dinickel paddle-wheel complexes (2.4846(8) and 2.3753(5) A in 5 and 7 respectively) is defined by the geometric parameters of the bidentate ligands and that intermetal bonding is not present.

Expanding the tools available for direct ortho cupration – targeting lithium phosphidocuprates

Reaction of in situ generated lithium phosphides with 0.5 eq. Cu(I) is employed as a means of targeting lithium phosphidocuprates of either Gilman- or Lipshutz-type formulation--e.g., (R(2)P)(2)CuLi·n(LiX) (n = 0, 1). For R = Ph, X = CN in toluene followed by thf or R = Ph, X = I in thf/toluene an unexpected product results. [(Ph(2)P)(6)Cu(4)][Li·4thf](2)1 reveals an ion-separated structure in the solid state, with solvated lithium cations countering the charge on an adamantyl dianion [(Ph(2)P)(6)Cu(4)](2-). Deployment of R = Ph, X = CN in thf affords a novel network based on the dimer of Ph(2)PCu(CN)Li·2thf 2 with trianions based on 6-membered (PCu)(3) rings acting as nodes in the supramolecular array and solvated alkali metal counter-ions completing the linkers. Cy(2)PLi (Cy = cyclohexyl) has been reacted with CuCN in thf/toluene to yield Gilman-type lithium bis(phosphido)cuprate (Cy(2)P)(2)CuLi·2thf 3 by the exclusion of in situ generated LiCN. A polymer is noted in the solid state.

The redox effect of the [1,2-(NH)2C6H4]2− ligand in the formation of transition metal compounds

Reactions of the [1,2-(NH)(2)C(6)H(4)](2-) dianion (LH(2)(2-)) with Cp(2)M(II) (M = V, Mn) lead to complete or partial oxidation of the metals (M), giving the V(III) compound [(η(5)-Cp)(LH(2))(2)VV(LH(2))](-)[Li(THF)(4)](+) (1) and Mn(II)(4)Mn(III)(2) oxo cage [Mn(6)(LH(2))(6)(μ(6)-O)(THF)(4)] (2).

Chapter 6:Alkali/Coinage metals – organolithium, organocuprate chemistry

This chapter covers the literature on group 1 and 11 organometallics, primarily those that contain a carbon-metal bond, in the years 2011 and 2012. In the first part, coordination compounds of the alkali metals are discussed. We look firstly at organolithiums and then cover compounds of the higher alkali metals. Sandwich compounds are discussed, including significant new work that relates to lithium-coordinated reduced corannulene systems. The use of other aryl ligands, as well as alkyl, alkynyl, carbenoid and N-donor ligands is also discussed. Compounds of the coinage metals - copper, silver and gold - are considered in the second part of the review. Discussion is broken down by metal, starting with copper. The first efficient synthesis of (Ph3P)3CuCF3 is reported, as are related studies on “CuCF3” derivatives. Other copper systems to have been looked at in 2011/12 include those with aryl, phosphorus- and sulfur-donor ligands. A large number of studies on carbenoid complexes are also reviewed. This interest in carbene chemistry is also reflected within the silver and gold sections that follow, with alkynyl ligand chemistry also playing a major role in recent gold studies. For both groups 1 and 11, mixed-metal systems are also discussed as appropriate, including the development of synergic bases, new multiply-bonded transition metal complexes and luminescent group 11 clusters.