Keith Izod

Group I complexes of P- and as-donor ligands

Publisher Summary This chapter presents range of phosphorus (P)- and arsenic (As)-containing ligands, with emphasis on those complexes in which there is an established contact between phosphorus or arsenic and an alkali metal. 31 P NMR spectroscopy is an invaluable tool for identifying and studying M–P interactions, particularly in solution, and for complexes with a Li–P contact 31 P and 6 Li/ 7 Li NMR studies can provide a wealth of structural and thermodynamic information. However, X-ray crystallography is unrivaled as a technique for elucidating the nature of species in the solid state. For this reason, largely it is focused on complexes in which a P–M or As–M contact has been verified by crystallography. The low affinity of the alkali metals for P- and As-donors is overcome by incorporating the P- or As-donor site into an anionic ligand. The chapter illustrates the wide structural diversity among group 1 complexes of P- and As-donor ligands. The structures of such compounds are highly sensitive to the nature of the metal center, the ligand substituents, the presence and nature of coligands, and the presence of functional groups at the ligand periphery.

Complexes of P-stabilised carbanions with s- and p-elements

Abstract The chemistry of complexes of the main group metals (Groups 1, 2, 13, 14, and 15, including Si and As) with P-stabilised carbanions is described. Such ligands, in which a carbanion centre is immediately adjacent to a P(III) or P(V) centre are remarkably versatile and adopt a wide range of coordination modes, depending on the nature of the metal centre, the presence of co-ligands and the ligand substituents; certain main group derivatives have also found applications in organic synthesis, especially for the olefination of carbonyl compounds (Horner, or Horner–Wadsworth–Emmons reagents). The focus of the review is on complexes which have been structurally characterised, either by crystallographic means or by unambiguous spectroscopic evidence.

Synthesis, structure and reactions of organometallic compounds of Groups 1–3 containing bulky silicon-substituted alkyl groups

Abstract A review is presented of the chemistry of organometallic compounds containing very bulky ligands of the types C(SiMe 2 X) 3 (X = Me, Ph or OMe) and C(SiMe 3 ) 2 (SiMe 2 X) (X = Ph or OMe) attached to metals of Groups 1–3. The structures and reactions of these compounds show novel features not observed for analogues containing less bulky alkyl groups.

Germanium(II) and tin(II) complexes of a sterically demanding phosphanide ligand.

The reaction between PhPCl(2) and 1 equiv of RLi, followed by in situ reduction with LiAlH(4) and an aqueous workup yields the secondary phosphane PhRPH [R = (Me(3)Si)(2)CH]. Treatment of PhRPH with n-BuLi in diethyl ether generates the lithium phosphanide (RPhP)Li(Et(2)O)(n) [15(Et(2)O)], which may be crystallized as the tetrahydrofuran (THF) adduct (RPhP)Li(THF)(3) [15(THF)]. Compound 15(Et(2)O) reacts with 1 equiv of either NaO-tBu or KO-tBu to give the corresponding sodium and potassium phosphanides (RPhP)Na(Et(2)O)(n) (16) and (RPhP)K(Et(2)O)(n) (17), which may be crystallized as the amine adducts [(RPhP)Na(tmeda)](2) [16(tmeda)] and [(RPhP)K(pmdeta)](2) [17(pmdeta)], respectively. The reaction between 2 equiv of 17 and GeCl(2)(1,4-dioxane) gives the dimeric compound [(RPhP)(2)Ge](2).Et(2)O (18.Et(2)O). In contrast, the reaction between 2 equiv of 15 and SnCl(2) preferentially gives the ate complex (RPhP)(3)SnLi(THF) (19) in low yield; 19 is obtained in quantitative yield from the reaction between SnCl(2) and 3 equiv of 15. Crystallization of 19 from n-hexane/THF yields the separated ion pair complex [(RPhP)(3)Sn][Li(THF)(4)] (19a); exposure of 19a to vacuum for short periods leads to complete conversion to 19. Treatment of GeCl(2)(1,4-dioxane) with 3 equiv of 15 yields the contact ion pair (RPhP)(3)GeLi(THF) (20), after crystallization from n-hexane/THF. Compounds 15(THF), 16(tmeda), 17(pmdeta), 18.Et(2)O, 19a, and 20 have been characterized by elemental analyses, multielement NMR spectroscopy, and X-ray crystallography. While 15(THF) is monomeric, both 16(tmeda) and 17(pmdeta) are dimeric in the solid state. The diphosphagermylene 18.Et(2)O adopts a dimeric structure in the solid state with a syn,syn-arrangement of the phosphanide ligands, and this structure appears to be preserved in solution. The ate complex 19a crystallizes as a separated ion pair, whereas the analogous ate complex 20 crystallizes as a discrete molecular species. The structures of 19 and 20 are retained in non-donor solvents, while dissolution in THF yields the separated ion pairs 19a and [(RPhP)(3)Ge][Li(THF)(4)] (20a).

Pyridine-functionalized metal alkyls—II. Synthesis, crystal structures and electronic properties of first-row transition metal 2-pyridino(bistrimethylsilyl)methyls and 2-pyridino(trimethylsilyl)methyls

Abstract The new chromium(II), manganese(II), iron(II) and cobalt(II) alkyls derived from the anions of 2-bis(trimethylsilyl)methylpyridine (Hbtsmp) and 2-trimethylsilymethylpyridine (Htsmp) are described. X-ray crystal structures show that [M(btsmp) 2 ] (M  Cr, Co) have square-planar geometry, but that [Fe(btsmp) 2 ] has a distorted tetrahedral structure. Magnetochemical studies show [Mn(btsmp) 2 ] exhibits a 2 E − 6 A spin state equilibrium. Solid-state effects are discussed in the interpretation of differences between solid and solution state magnetochemical data of the Cr and Co compounds of btsmp. The ESR spectrum of the latter is also analysed. Reactions of CO and Bu t NC with the Cr and Co compounds are described. Evidence for the formation of a zirconium(III) species from 2-methylpyridine is assessed.

Synthesis, properties and X-ray crystal structures of copper(II) and nickel(II) thiocyanate complexes with ethanolamine : a new structure for an aminoalkoxide cluster

Abstract The new antiferromagnetic polymer [Cu(NH2C2H4O)(NCS)]∞ has been prepared and shown by X-ray crystallography to contain a new polymeric linkage of pairs of copper(II) atoms linked alternately by two oxygen bridges and one weaker thiocyanate bridge. Electronic, ESR and IR spectra and temperature-variable magnetochemical data are described. [Ni(NH2C2H4OH)2(NCS)2] is fully characterized by its magnetism, electronic and IR spectra and crystal structure as a centrosymmetric octahedral monomer with nitrogen-coordinated thiocyanates.

Stabilization of a Diphosphagermylene through pπ–pπ Interactions with a Trigonal‐Planar Phosphorus Center

N-Heterocyclic carbenes and their heavier homologues are, in part, stabilized by delocalization of the N lone pairs into the vacant p-orbital at carbon (or a heavier Group 14 element center). These interactions are usually absent in the corresponding P-substituted species, owing to the large barrier to planarization of phosphorus. However, judicious selection of the substituents at phosphorus has enabled the synthesis of a diphosphagermylene, [(Dipp)2P]2 Ge, in which one of the P centers is planar (Dipp=2,6-diisopropylphenyl). The planar nature of this P center and the correspondingly short P-Ge distance suggest a significant degree of P-Ge multiple bond character that is due to delocalization of the phosphorus lone pair into the vacant p-orbital at germanium. DFT calculations support this proposition and NBO and AIM analyses are consistent with a Ge-P bond order greater than unity.

Oxidation reactions of a phosphine-borane-stabilised dialkylstannylene

The acyclic dialkylstannylene [(Me(3)Si){Me(2)P(BH(3))}CH](2)Sn (7) reacts with any of methyl iodide, neopentyl iodide or benzyl bromide to yield the corresponding oxidative addition products [(Me(3)Si){Me(2)P(BH(3))}CH](2)Sn(Me)(I) (8), [(Me(3)Si){Me(2)P(BH(3))}CH](2)Sn(CH(2)CMe(3))(I) (9), and [(Me(3)Si){Me(2)P(BH(3))}CH](2)Sn(CH(2)Ph)(Br) (10), respectively. The crystal structures of 8, 9, and 10 reveal that there are no close B-H...Sn contacts. In addition, 7 reacts with benzil or elemental sulfur to yield [{Me(2)P(BH(3))}(Me(3)Si)CH](2)Sn(OCPh=CPhO) (11) and [{Me(2)P(BH(3))}(Me(3)Si)CH](2)Sn(S) (12), respectively, as confirmed by multinuclear NMR spectroscopy and elemental analysis.

Synthesis and structural characterisation of alkali metal complexes of heteroatom-stabilised 1,4- and 1,6-dicarbanions

A straightforward Peterson olefination reaction between either [{(Me(2)PhSi)(3)C}Li(THF)] or in situ-generated [(Me(3)Si)(2){Ph(2)P(BH(3))}CLi(THF)(n)] and paraformaldehyde gives the alkenes (Me(2)PhSi)(2)C[double bond, length as m-dash]CH(2) () and (Me(3)Si){Ph(2)P(BH(3))}C[double bond, length as m-dash]CH(2) (), respectively, in good yield. Ultrasonic treatment of with lithium in THF yields the lithium complex [{(Me(2)PhSi)(2)C(CH(2))}Li(THF)(n)](2) (), which reacts in situ with one equivalent of KOBu(t) in diethyl ether to give the potassium salt [{(Me(2)PhSi)(2)C(CH(2))}K(THF)](2) (). Similarly, ultrasonic treatment of with lithium in THF yields the lithium complex [[{Ph(2)P(BH(3))}(Me(3)Si)C(CH(2))]Li(THF)(3)](2).2THF (). The bis(phosphine-borane) [(Me(3)Si){Me(2)(H(3)B)P}CH(Me(2)Si)(CH(2))](2) () may be prepared by the reaction of [Me(2)P(BH(3))CH(SiMe(3))]Li with half an equivalent of ClSiMe(2)CH(2)CH(2)SiMe(2)Cl in refluxing THF. Metalation of with two equivalents of MeLi in refluxing THF yields the lithium complex [[{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}]Li(THF)(3)](2) (), whereas metalation with two equivalents of MeK in cold diethyl ether yields the potassium complex [[{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}](2)K(2)(THF)(4)](infinity) () after recrystallisation. X-Ray crystallography shows that, whereas the lithium complex crystallises as a discrete molecular species, the potassium complexes and crystallise as sheet and chain polymers, respectively.

Pyridine functionalized alkyls of transition metals. Synthesis of bis[C,N-2-pyridylbis(trimethylsilyl)methyl]nickel

Abstract Alternate lithiation and reaction with ClSiMe3 of 2,6-dimethylpyridine gave the lithium derivatives of pyridine substituted at the 2- and 6-positions by mono- or bis(trimethylsilyl)methyl groups. The relative ease of formation of these compounds is discussed and compared to their reactivity with transition metal halides. The reaction of NiCl2 with the lithium derivative of bis(trimethylsilyl)methylpyridine gives the remarkably air-stable nickel(II) alkyl bis[C,N-2-pyridylbis(trimethylsilyl)methyl]nickel(II).