Alkali metal reduction of crown ether encapsulated alkali metal cations.

[{SiNDipp}BeClM]2 ({SiNDipp} = {CH2SiMe2N(Dipp)}2; M = Li, Na, K, Rb) are converted to ionic species by treatment with a crown ether. Whereas the lithium derivative reacts with Na or K to provide [{SiNDipp}BeCl]-[M(12-cr-4)2]+ (M = Na, K), the resultant sodium species is resistant to reduction by potassium. These observations are rationalised by a hybrid experimental/theoretical analysis.

Pathway to a molecular calcium methyl.

The dimeric ß-diketiminato calcium hydride, [(BDI)CaH]2 (BDI = HC{(Me)CN-2,6-iPr2C6H3}2), reacts with ZnMe2 to afford the bimetallic calcium zincate complex, [(BDI)Ca(µ-CH3)2Zn(µ-H)]2, which subsequently undergoes an intramolecular reaction to effect the formation of [(BDI)CaMe]2, a notable omission from the homologous series of ß-diketiminato alkylcalcium derivatives.

From alkaline earth to coinage metal carboranyls.

The ß-diketiminato calcium and magnesium complexes, [(BDI)MgnBu] and [(BDI)CaH]2 (BDI = HC{C(Me)NDipp}2; Dipp = 2,6-di-isopropylphenyl), react with ortho-carborane (o-C2B10H12) to provide the respective [(BDI)Ae(o-C2B10H11)] (Ae = Mg or Ca) complexes. While the lighter group 2 species is a monomer with magnesium in a distorted trigonal planar environment, the heavier analogue displays a puckered geometry at calcium in the solid state due to Ca⋯H-B intermolecular interactions. These secondary contacts are, however, readily disrupted upon addition of THF to provide the 4-coordinate monomer, [(BDI)Ca(THF)(o-C2B10H11)]. [(BDI)Mg(o-C2B10H11)] was reacted with [NHCIPrMCl] (NHCIPr = 1,3-bis(isopropyl)imidazol-2-ylidene; M = Cu, Ag, Au) to provide [NHCIPrM(o-C2B10H11)], rare C-bonded examples of coinage metal derivatives of unsubstituted (o-C2B10H11)- and confirming the alkaline earth compounds as viable reagents for the transmetalation of the carboranyl anion.

Cesium Reduction of a Lithium Diamidochloroberyllate.

Room temperature reaction of elemental cesium with the dimeric lithium chloroberyllate [{SiNDipp}BeClLi]2 [{SiNDipp} = {CH2SiMe2N(Dipp)}2, where Dipp = 2,6-di-isopropylphenyl, in C6D6 results in activation of the arene solvent. Although, in contrast to earlier observations of lithium and sodium metal reduction, the generation of a mooted cesium phenylberyllate could not be confirmed, this process corroborates a previous hypothesis that such beryllium-centered solvent activation also necessitates the formation of hydridoberyllium species. These observations are further borne out by the study of an analogous reaction performed in toluene, in which case the proposed generation of formally low oxidation state beryllium radical anion intermediates induces activation of a toluene sp3 C-H bond and the isolation of the polymeric cesium benzylberyllate, [Cs({SiNDipp}BeCH2C6H5)]∞.

Alkali metal reduction of alkali metal cations.

Counter to synthetic convention and expectation provided by the relevant standard reduction potentials, the chloroberyllate, [{SiNDipp}BeClLi]2 [{SiNDipp} = {CH2SiMe2N(Dipp)}2; Dipp = 2,6-i-Pr2C6H3)], reacts with the group 1 elements (M = Na, K, Rb, Cs) to provide the respective heavier alkali metal analogues, [{SiNDipp}BeClM]2, through selective reduction of the Li+ cation. Whereas only [{SiNDipp}BeClRb]2 is amenable to reduction by potassium to its nearest lighter congener, these species may also be sequentially interconverted by treatment of [{SiNDipp}BeClM]2 by the successively heavier group 1 metal. A theoretical analysis combining density functional theory (DFT) with elemental thermochemistry is used to rationalise these observations, where consideration of the relevant enthalpies of atomisation of each alkali metal in its bulk metallic form proved crucial in accounting for experimental observations.

Variable Ca-Caryl Hapticity and its Consequences in Arylcalcium Dimers.

The dimeric ß-diketiminato calcium hydride, [(Dipp BDI)CaH]2 (Dipp BDI = HC{(Me)CN-2,6-i-Pr2 C6 H3 }2 ), reacts with ortho-, meta- or para-tolyl mercuric compounds to afford hydridoarylcalcium compounds, [(Dipp BDI)2 Ca2 (µ-H)(µ-o-,m-,p-tolyl)], in which dimer propagation occurs either via µ2 -η1 -η1 or µ2 -η1 -η6 bridging between the calcium centers. In each case, the orientation and hapticity of the aryl units is dependent upon the position of the methyl substituent. While wholly organometallic meta- and para-tolyl dimers, [(Dipp BDI)Ca(m-tolyl)]2 and [(Dipp BDI)Ca(p-tolyl)]2 , can be prepared and are stable, the ortho-tolyl isomer is prone to isomerization to a calcium benzyl analog. Computational analysis of this latter process with density functional theory (DFT) highlights an unusual mechanism invoking the generation of an intermediate dicalcium species in which the group 2 centers are bridged by a toluene dianion formed by the formal attachment of the original hydride anion to the initially generated ortho-tolyl substituent. Use of a more sterically encumbered aryl substituent, {3,5-t-Bu2 C6 H3 }, facilitates the selective formation of [(Dipp BDI)Ca(µ-H)(µ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)], which can be converted into the unsymmetrically-substituted σ-aryl calcium complexes, [(Dipp BDI)Ca(µ-Ph)(µ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)] and [(Dipp BDI)Ca(µ-p-tolyl)(µ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)] by reaction with the appropriate mercuric diaryl. Conversion of [(Dipp BDI)Ca(H)(Ph)Ca(Dipp BDI)] to afford [{{(Dipp BDI)Ca}2 (µ2 -Cl)}2 (C6 H5 -C6 H5 )], comprising a biphenyl dianion, is also reported. Although this latter transformation is serendipitous, AIM analysis highlights that, in a related manner to the ortho-tolyl to benzyl isomerization, the requisite C-C coupling may be facilitated in an "across dimer" fashion by the experimentally-observed polyhapto engagement of the aryl substituents with each calcium.

Beryllium-centred C-H activation of benzene.

Reaction of BeCl2 with the dilithium diamide, [{SiNDipp}Li2] ({SiNDipp} = {CH2SiMe2NDipp}2), provides the dimeric chloroberyllate, [{SiNDippBeCl}Li]2, en route to the 2-coordinate beryllium amide, [SiNDippBe]. Lithium or sodium reduction of [SiNDippBe] in benzene, provides the relevant organoberyllate products, [{SiNDippBePh}M] (M = Li or Na), via the presumed intermediacy of transient Be(I) radicals.

Synthesis of Molecular Phenylcalcium Derivatives: Application to the Formation of Biaryls.

Hydrocarbon-soluble ß-diketiminato phenylcalcium derivatives, which display various modes of Ca-µ2 -Ph-Ca bridging, are accessible from reactions of Ph2 Hg and [(BDI)CaH]2 . Although the resultant compounds are inert toward the C-H bonds of benzene, they yield selective and uncatalyzed biaryl formation when reacted with readily available aryl bromides.

A Benzodiphosphaborolediide.

The first example of a diphosphaborolediide, the benzo-fused [C6 H4 P2 BPh]2- (12- ), is prepared from ortho-bis(phosphino)benzene (C6 H4 {PH2 }) and dichlorophenylborane, via a sequential lithiation approach. The dilithio-salt can be obtained as an oligomeric THF solvate or discrete TMEDA adduct, both of which are fully characterized, including by X-ray diffraction. Alongside NICS calculations, data strongly suggest some aromaticity within 12- , which is further supported by preliminary coordination studies that demonstrate η5 -coordination to a zerovalent molybdenum center, as observed crystallographically for the oligomeric [{Mo(CO)3 (η5 -1)}{µ-η1 -Mo(CO)3 (TMEDA)}2 ] ⋅ [µ-Li(THF)][µ-Li(TMEDA)].

Diphosphametacyclophanes: Structural and Electronic Influences of Substituent Variation within a Family of Bis(diketophosphanyl) Macrocycles.

The condensation of MeP(SiMe3)2 with a series of 5-substituted isophthaloyl chlorides (5-R'C6H3-2,6-{C(O)Cl}2) affords the diphosphametacyclophanes m-{-C(O)-C6H3-5-R'-(C(O)PMe)}2 (R' = I, Me, tBu, Ph, and p-NCC6H4); the analogues m-{-C(O)-C5H3N-(C(O)PMe)}2 and m-{-C(O)-C6H4-(C(O)PPh)}2 are similarly obtained in preference to higher oligomers, in contrast to precedent reports. The cyclophanes all adopt butterfly-like conformations in the solid state with the P-organyl substituents adopting mutually exo arrangements. Structural and computational data suggest the nature of the 5-R substituent is key in directing the inter-ring angle and the extent of LUMO stabilization about the diketophophanyl scaffold. The latter is substantiated by UV/vis spectroscopy and cyclic voltammetry, which demonstrate these cyclophanes to be appreciably comparable to the diketophosphanyl systems commonly explored in the context of organic electronic materials; intriguingly, the distinct dikeophosphanyl moieties within the macrocycles appear effectively "insulated" by the macrocycle geometry, rather than acting as a through-conjugate.

Phosphacycloalkyldiones: synthesis and coordinative behaviour of 6- and 7-member cyclic diketophosphanyls.

Glutaryl and adipoyl chlorides undergo facile condensation with the bis(silyl)phosphanes RP(SiMe3)2 (R = Me, nBu, tBu, Ph, Mes) to afford exclusively the phosphacycloalkyldiones (CH2)n(C[double bond, length as m-dash]O)2PR (n = 3, 4). Characterised spectroscopically and, for R = Ph, Mes (n = 3) crystallographically, the macrocycles are conformationally fluxional in solution and appreciably moisture sensitive. Though seemingly resistant to chemical oxidation at phosphorus, coordination is readily achieved, as illustrated by isolation of trans-[Pt(PEt3){P(Ph)(CO)2(CH2)3}Cl2] and a series of tungsten pentacarbonyl complexes, which are characterised crystallographically and by infrared and NMR spectroscopy. Together, these data suggest the macrocycles to be relatively weak σ-donors with no appreciable π-acceptor character.

Controlled Reactivity of Terminal Cyaphide Complexes: Isolation of the 5-Coordinate [Ru(dppe)2(C≡P)].

The novel cyaphide complex trans-[Ru(dppe)2Me(C≡P)] is obtained in excellent yields and exhibits the first instance of controlled reactivity of any terminal cyaphide complex. Its treatment with ZnX2/PPh3 effects selective metathesis of the methyl moiety to afford the unprecedented halocyaphide complexes trans-[Ru(dppe)2(X)(C≡P)] (X = Cl, Br, I), which are structurally characterized (X = Cl, Br). Exemplified with the trans-bromide, these compounds are susceptible to substitution of the halides by nucleophilic reagents-illustrated with Me2Mg-and also readily undergo halide abstraction by TlOTf to afford the first hypocoordinate cyaphide complex, viz., [Ru(dppe)2(C≡P)]·OTf, which is isolable in bulk and exhibits good stability. NMR spectroscopic and crystallographic data reveal the latter to adopt a square-pyramidal geometry with an accessible coordinate vacancy, which is susceptible to the addition of nucleophiles. This is illustrated analytically by reactions with Me2Mg and LiC≡CPh and with its facile bulk carbonylation to afford trans-[Ru(dppe)2(CO)(C≡P)]+.

Exploring the Reactivity of Donor-Stabilized Phosphenium Cations: Lewis Acid-Catalyzed Reduction of Chlorophosphanes by Silanes.

Phosphane-stabilized phosphenium cations react with silanes to effect either reduction to primary or secondary phosphanes, or formation of P-P bonded species depending upon counteranion. This operates for in situ generated phosphenium cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence studies have allowed insight into the competing mechanisms involved.

Donor-substituted phosphanes - surprisingly weak Lewis donors for phosphenium cation stabilisation.

Paradoxically, N- and O-donor substituted tri-arylphosphanes are shown to be weaker donors than PPh3 when binding the soft Lewis acid moiety [PPh2]+. This arises from internal solvation and rehybridisation at phosphorus, precluding chelation and increasing steric demand, in direct contrast to coordination modes observed for metal complexes.

The Community Dental Facilitator Project: reducing barriers to dental care.

OBJECTIVES: This report describes an initiative developed and implemented by a low-income, urban, Canadian community to respond to their children's dental problems. METHODS: The first strategy pursued by the community was the development of the Community Dental Facilitator Project. This project facilitated children's access to existing government funding for dental treatment, and subsequently facilitated access to treatment at local dental offices. Children in need of treatment were identified by a school dental screening. The facilitation work was done by three lay workers hired from within the community who represented the community's predominant ethnic groups. RESULTS: Parents revealed that barriers to dental care in local dental offices were lack of information about funding programs, language, inflexible work situation, and mistrust of bureaucracy. By the project's end, with the assistance of the facilitators, a significantly increased number of children had been enrolled for government dental benefits (P<.001). In addition to the 123 children identified at the screening as needing treatment, another 30 children "self-referred" to the program. At the end of the project's original funding period, dental appointments had been made for 68 children: 60 (48.8%) of the "screened" group, 8 (26.7%) of the "self-referred" group. One-year telephone follow-up to parents of the screened children revealed that 42 of 59 (71.1%) had completed treatment. CONCLUSIONS: Barriers to dental care for low-income children go beyond economics. A community facilitation model can improve low-income children's access to existing dental services and may reduce the barriers to care for some children requiring treatment.