Robert Haigh

The structural characteristics of organozinc complexes incorporating N,N′-bidentate ligands

Dimethylzinc reacts with an excess of N-2-pyridylaniline 6 to give the homoleptic species, Zn[PhN(2-C(5)H(4)N)](2) 8. Single crystal X-ray diffraction reveals a solid-state dimer based on an 8-membered (NCNZn)(2) core motif. Zn[CyN(2-C(5)H(4)N)]Me (Cy =c-C(6)H(11)) 10, prepared by the combination of ZnMe(2) with the corresponding cyclohexyl-substituted pyridylamine, is also dimeric in the solid state but reveals a central (ZnN)(2) metallacycle. Employment of (p-Tol)NH(2-C(5)H(4)N)(p-Tol = 4-MeC(6)H(4)) 11 yielded the tris(zinc) adduct Zn(3)[(p-Tol)N(2-C(5)H(4)N)](4)Me(2) 12, which incorporates a central chiral molecule of Zn[(p-Tol)N(2-C(5)H(4)N)](2) 12a, that bridges two Zn[(p-Tol)N(2-C(5)H(4)N)]Me 12b units. A similar trimetallic structure is noted when the pyridylaniline substrate 11 is replaced with the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), affording Zn(3)(hpp)(4)Me(2) 13. Spectroscopic studies point to retention of the solid-state structure of in hydrocarbon solution. Reaction of 13 with dimesityl borinic acid, Mes(2)BOH (Mes = mesityl), affords Zn(3)(hpp)(4)(OBMes(2))(2) 14 in which the trimetallic core is retained. This reactivity is in contrast to the closely related reaction of dimeric Zn[Me(2)NC[N(i)Pr](2)]Me 15 with Mes(2)BOH, which yielded Zn[Me(2)NC[N(i)Pr](2)][OBMes(2)].Me(2)NC[N(i)Pr][NH(i)Pr] 16 as a result of protonation at the guanidine ligand in addition to the Zn-Me bond.

Synthesis and structure of [{Sn(μ‒PCy)}3(Na·PMDETA)2], containing an electron-deficient [{Sn(μ‒PCy)}3]2- dianion

The reaction of CyPHNa with Sn(NMe2)2 in the presence of PMDETA (= n{Me2NCH2CH2}2NMe) gives the title compound [{Sn(μ–PCy)}3(Na·PMDETA)2] n(1), containing an electron-deficient [(Sn(μ–PCy)}]32− dianion with a novel two-electron, three centre (2e–3c) bonding arrangement.

Oxygen scavenging by lithium zincates: the synthesis, structural characterisation and derivatisation of [Ph(2-C5H4N)N]2ZnRLi·nthf (R = But, Bun; n= 1, 2)

The 1 ∶ 2 reaction of ZnMe2 with N-2-pyridylaniline, Ph(2-C5H4N)NH 1, affords [Ph(2-C5H4N)N]2Zn 10, the treatment of which with BuLi and thf affords the diastereomeric lithium zincate [Ph(2-C5H4N)N]2ZnRLi·nthf (R = Bun, n n= 2; 11a; R = But, n n= 1, 11b). The sequential treatment of 10 (either in situ or after isolation) with organolithium substrates and molecular oxygen has afforded insights into the oxygen-scavenging capacity of mixed Group 1–Group 12 species. Hence, 10 reacts with BunLi, O2 nand thf or dimethoxyethane (dme) to give {[Ph(2-C5H4N)N]2ZnOBunLi·nL}2 (n n= 1, L = thf, 12a; n n= 0.5, L = dme, 12b), with the structural relationship between 11a and 12a strongly suggesting that for R = Bun oxygenation proceeds by insertion into the Zn–C bond of an {[Ph(2-C5H4N)N]2ZnR}− ion. The employment of ButLi, O2 and thf together with 10 affords only the previously reported complex [Ph(2-C5H4N)N]2Zn[(μ3-O)But]2(Li·thf)24, nthe formation of which may be rationalised in terms of the But van der Waals radius and cone angle.

Synthesis and structure of [{MeAl(μ-PMes)(PMes)}2Li4]2·7thf, containing a [MeAl(μ-PMes)(PMes)]24− tetraanion (Mes = 2,4,6-Me3C6H2)

The reaction of MeAlCl2 with MesPHLi (1∶4 equivalents) in thf/toluene gives the cage complex [{MeAl(μ-PMes)(PMes)}2Li4]2·7thf (1), containing an [{MeAl(μ-PMes)(PMes)}2]4− tetraanion which is valence-isoelectronic with extensively studied Group 15 anions of the type [E(μ-NR)(NR)]22−

Toward an understanding of the oxygen scavenging properties of lithium zincates

The reaction of ZnMe2 with 2-pyridylamine [HN(2-C5H4N)Ph 1], LitBu and thereafter with dry air has concomitantly yielded {[Ph(2-C5H4N)N]2ZnOMeLi·thf}2 (2) and [Ph(2-C5H4N)N]2Zn[(μ3-O) Bu]2(Li·thf)2 (3). The structure of 2 implies the insertion of oxygen into a [(R2N)2ZnMe]– ion. To probe this mechanism, we have prepared, characterized, and derivatized [Ph(2-C5H4N)N]2ZnRLi (R = nBu, n = 2, L = thf, 4a; R = tBu, n = 1, L = thf, 4b) (Figure 1). The sequential reaction of [Ph(2-C5H4N)N]2Zn with nBuLi, thf and O2 gives {[Ph(2C5H4N)N]2ZnOBuLi·nL}2 (n = 1, L = thf, 5), the structures of 4a and 5 strongly suggesting that oxygenation proceeds by insertion into the Zn C bond of an {[Ph(2-C5H4N)N]2ZnnBu}– ion. The treatment of [Ph(2-C5H4N)N]2Zn with tBuLi, thf, and O2 affords only the previously reported 3—this being in part rationalized in terms of the steric requirements of OtBu. Moreover, the structure of 3 is closely related to that of 5. Formally, this can be described in terms of the rearrangement of M O (M = Li, Zn) interactions in response to the presence or absence of a [Ph(2-C5H4N)N]2Zn moiety. Structural characterization of {[Ph(2-C5H4N)N]2ZnBuLi·dme}(6), {[Ph(2-C5H4N)N]2ZnOBuLi·0.5dme}2 (7), and [Ph(2-C5H4N)N]2 Zn[(μ3-O)Bu]2(Li2·dme) (8), further support this postulated oxygen insertion.

New motifs in lithium zincate chemistry: a solid-state structural study of PhC(O)N(R)ZnR′2Li·2thf (R, R′ = alkyl, aryl) and [PhC(O)N(Ph)Li·thf]·[PhC(O)N(Ph)Zn(But)2Li·thf]

The facile reaction of ZnMe2 with secondary carboxylic amides of the type PhC(O)N(R)H (R = Me 14, Pri15, Ph 16) yields PhC(O)N(R)ZnMe (R = Me 17, Pri18, Ph 19). These complexes describe a hexamer (for 17) and tetramers (for 18 and 19) in the solid state which are best viewed as stacks of cyclic trimers and dimers, respectively. In turn, 17–19 react with ButLi to afford either the lithium zincate PhC(O)N(R)Zn(But)2Li·2thf (R = Me 20, Pri21) or the co-complex [PhC(O)N(Ph)Li·thf]·[PhC(O)N(Ph)Zn(But)2Li·thf] n22. In the solid state both 20 and 21 reveal dimeric structures based on a (LiO)2 core in which each alkali metal centre is doubly thf-solvated and trivalent zinc centres reside peripheral to the cluster. The structure of 22 reveals an adduct in which a dimeric lithium (carboxylic) amide core interacts with two PhC(O)N(Ph)Zn(But)2Li molecules, affording a structure intermediate between a ladder and an “open” pseudo-cubane. This is the first full characterisation of a complex between an alkali metal zincate and another organometallic species and it affords new insights into how these two classes of molecule interact. The straightforward formation of [PhC(O)N(R)ZnMe2]− n(R = Me 23, Ph 24) ions has been successfully achieved by treating the appropriate lithium carboxylic amide with ZnMe2. In the solid-state, PhC(O)N(Ph)ZnMe2Li·2thf 24 is revealed to be isostructural with 20 and 21.