Joanna Haywood

Mixed alkylamido aluminate as a kinetically controlled base.

The mechanisms by which directed ortho metalation (DoM) and postmetalation processes occur when aromatic compounds are treated with mixed alkylamido aluminate i-Bu3Al(TMP)Li (TMP-aluminate 1; TMP = 2,2,6,6-tetramethylpiperidide) have been investigated by computation and X-ray diffraction. Sequential reaction of ArC(=O)N(i-Pr)2 (Ar = phenyl, 1-naphthyl) with t-BuLi and i-Bu3Al in tetrahydrofuran affords [2-(i-Bu3Al)C(m)H(n)C(=O)N(i-Pr)2]Li x 3 THF (m = 6, n = 4, 7; m = 10, n = 6, 8). These data advance the structural evidence for ortho-aluminated functionalized aromatics and represent model intermediates in DoM chemistry. Both 7 and 8 are found to resist reaction with HTMP, suggesting that ortho-aluminated aromatics are incapable of exhibiting stepwise deprotonative reactivity of the type recently shown to pertain to the related field of ortho zincation chemistry. Density functional theory calculations corroborate this view and reveal the existence of substantial kinetic barriers both to one-step alkyl exchange and to amido-alkyl exchange after an initial amido deprotonation reaction by aluminate bases. Rationalization of this dichotomy comes from an evaluation of the inherent Lewis acidities of the Al and Zn centers. As a representative synthetic application of this high kinetic reactivity of the TMP-aluminate, the highly regioselective deprotonative functionalization of unsymmetrical ketones both under mild conditions and at elevated temperatures is also presented.

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]

A quadruply-bonded [Cr2(guanidinate)4]4−tetraanion

The reaction of chromocene, Cp(2)Cr, with dilithiated 2,3-diphenylguanidine [(PhNH)(2)C=NH = L(2)H(3)] gives the novel, quadruply-bonded tetraanion [Cr(2)(L(2)H)(4)](4-).

On the control of secondary carbanion structure utilising ligand effects during directed metallation

Summary N,N-Diisopropyl-2-propylbenzamide 6-H undergoes lateral deprotonation by t-BuLi in the presence of the Lewis base PMDTA (N,N,N′,N″,N″-pentamethyldiethylenetriamine) to give a benzyllithium 6-Lil·PMDTA that incorporates a trigonal planar secondary carbanion. In the solid state, the amide directing group and the PMDTA additive work together to abstract the metal ion from the deprotonated α-C of the propyl group (4.107(4) Å). A short distance of 1.376(3) Å is observed between the deprotonated carbon centre and a planar aromatic system that shows a pattern of bond lengths which contrasts with that reported for related tertiary carbanion systems. Analogous benzylic deprotonation is seen if 6-H is treated with t-BuLi in the presence of diglyme to give 6-Lil·DGME. X-ray crystallography now shows that the metal ion more closely approaches the tertiary carbanion (2.418(6) Å) but that the planarity of the deprotonated carbon centre and the bonding pattern in the organic anion seen in the PMDTA complex are retained. DFT analysis corroborates both the short distance between aromatic ring and carbanion centre and the unperturbed nature of aromaticity in 6-Lil·L (L = Lewis base). The observation of two structure-types for the carbanion in solution is explained theoretically and by NMR spectroscopy in terms of cis and trans isomerism imparted by partial double bond character in the arene–(α-C) bond.

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.

Alkali/coinage metals – organolithium, organocuprate chemistry

In Part 1 of this chapter, the alkali metal coordination compounds are reviewed, starting with mixed-metal ZnLi species, the interest in which has grown out of their synthetic importance as bases, and metallocene systems, including cyclopentadienyl derivatives. Cases of extreme interest notwithstanding, discussion is limited to compounds that contain at least one carbon-alkali metal interaction. Part 2 provides an overview of the latest developments in coinage metal organometallic chemistry. Aiming to reflect the balance between different areas of the most recent research, a review of copper-based metal-organic frameworks and coordination polymers is followed by compounds of more general interest. Similarly, for silver and gold, polymeric structures and coordination frameworks are described, along with carbene complexes and, for gold, phosphine complexes. As for Part 1, the emphasis is placed on systems that contain at least one carbon-metal interaction. The analytical discussion focuses on solid-state investigations and, where appropriate, applications are mentioned along with structural results.