The calcium-catalyzed intramolecular hydroamination of alkenes and alkynes is reported. The beta-diketiminato complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}-Ca{N(SiMe3)2}(THF)] affects catalytic cyclization of a range of aminoalkenes and aminoalkynes with activities that are broadly commensurate to those of established rare earth catalysts.

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The beta-diketiminate-stabilized calcium amide complex [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe(3))(2)}(THF)] (Ar = 2,6-diisopropylphenyl) and magnesium methyl complex [{ArNC(Me)CHC(Me)NAr}Mg(Me)(THF)] are reported as efficient precatalysts for hydroamination/cyclization of aminoalkenes. The reactions proceeded under mild conditions, allowing the synthesis of five-, six-, and seven-membered heterocyclic compounds. Qualitative assessment of these reactions revealed that the ease of catalytic turnover increases (i) for smaller ring sizes (5 > 6 > 7), (ii) substrates that benefit from favorable Thorpe-Ingold effects, and (iii) substrates that do not possess additional substitution on the alkene entity. Prochiral substrates may undergo diastereoselective hydroamination/cyclization depending upon the position of the existing stereocenter. Furthermore, a number of minor byproducts of these reactions, arising from competitive alkene isomerization reactions, were identified. A series of stoichiometric reactions between the precatalysts and primary amines provided an important model for catalyst initiation and suggested that these reactions are facile at room temperature, with the reaction of the calcium precatalyst with benzylamine proceeding with DeltaG(o)(298 K) = -2.7 kcal mol(-1). Both external amine/amide exchange and coordinated amine/amide exchange were observed in model complexes, and the data suggest that these processes occur via low-activation-energy pathways. As a result of the formation of potentially reactive byproducts such as hexamethyldisilazane, calcium-catalyst initiation is reversible, whereas for the magnesium precatalyst, this process is nonreversible. Further stoichiometric reactions of the two precatalysts with 1-amino-2,2-diphenyl-4-pentene demonstrated that the alkene insertion step proceeds via a highly reactive transient alkylmetal intermediate that readily reacts with N-H sigma bonds under catalytically relevant conditions. The results of deuterium-labeling studies are consistent with the formation of a single transient alkyl complex for both the magnesium and calcium precatalysts. Kinetic analysis of the nonreversible magnesium system revealed that the reaction rate depends directly upon catalyst concentration and inversely upon substrate concentration, suggesting that substrate-inhibited alkene insertion is rate-determining.

The Bi(3+) (N,C,N)-pincer complex Ar'BiCl(2) (1) [Ar' = 2,6-(Me(2)NCH(2))(2)C(6)H(3)], reacts with 2 equiv of KOC(6)H(3)Me(2)-2,6 and KOC(6)H(3)(i)Pr(2)-2,6 by ionic metathesis to form the anticipated bis(aryloxide) complexes Ar'Bi(OC(6)H(3)Me(2)-2,6)(2) (2) and Ar'Bi(OC(6)H(3)(i)Pr(2)-2,6)(2) (3), respectively. However, the analogous reaction with 2 equiv of KOC(6)H(3)(t)Bu(2)-2,6 forms HOC(6)H(3)(t)Bu(2)-2,6 and a dark-orange complex containing only one aryloxide-derived ligand bound via a Bi-C and not a Bi-O linkage. This complex is formulated as Ar'Bi(C(6)H(2)(t)Bu(2)-3,5-O-4) (4), a product of para C-H bond activation. Structural, spectroscopic, and DFT studies and a comparison with the protonated analogue [Ar'Bi(C(6)H(2)(t)Bu(2)-3,5-OH-4)][BPh(4)] (5), which was obtained by treatment of 4 with [HNEt(3)][BPh(4)], suggest that 4 contains an oxyaryl dianion. Complex 4 represents a fully characterizable product of a bismuth-mediated C-H activation and rearrangement of the type postulated in catalytic SOHIO processes.

The synthesis of magnesium and zinc complexes of bidentate anionic alkoxide ligands with saturated-backbone carbene groups is reported. Mono(ligand) and bis(ligand) complexes [M(L(R))N''](2) and [M(L(R))(2)] (M = Mg, Zn, N'' = N(SiMe(3))(2), L(R) = [OCMe(2)CH(2){CNCH(2)CH(2)NR}] R = (i)Pr, Mes, Dipp) have been isolated, and some structurally characterised and compared with the new unsaturated carbene complex [Mg(L)(2)]. Reactions with silyl halides show either addition across the metal carbene bond, or across the metal alkoxide bond, in accordance with the metals' electronegativity difference: the metal alkoxide bonds are stronger for Mg(II) complexes, for which the carbene is silylated to form zwitterionic [MgI(Me(3)SiL(R))N''] (Me(3)SiL(R) = OCMe(2)CH(2){Me(3)SiCNCH(2)CH(2)NR}) while the metal-bound alkoxide group is silylated in the Zn(II) complexes forming [ZnI(Me(3)SiOL(R))N''] (Me(3)SiOL(R) = Me(3)SiOCMe(2)CH(2){CNCH(2)CH(2)NR}). The proligand [HL(R)] is silylated at the alcohol group, forming the iodide salt [Me(3)SiOCMe(2)CH(2){HCNCH(2)CH(2)NR}]I.Preliminary results on the use of these complexes as initiators for the polymerisation of rac-lactide are reported, and suggest different initiation mechanisms are occurring for the two metals, in agreement with the different silylation reactivity observed. The polymerisation reactions are facile at room temperature even without an initiator, and yield polymers of reasonable molecular weight and heterotacticity and with good PDI. These are the first magnesium NHC complexes demonstrated to effect lactide polymerisation.Also, an adduct instead of the anticipated potassium alkoxycarbene is generated from the reaction of the proligand [HL(R)] with potassium amide KN''; this has been structurally characterised.

The tetravalent organometallic cerium complex [CeL4] is readily accessible from the oxidation of the trivalent [CeL3], L=a bidentate N-heterocyclic carbene alkoxide ligand, [C{(NPri)CHCHN}CH2CMe2O]. The [CeL4] complex should behave like the [UL4] analogue, but the two complexes show significantly different structures, highlighting the differences between 4f and 5f metals.

A new and modular route to bidentate ligands that combines an alkoxide with a saturated backbone N-heterocyclic carbene (NHC) is presented. The bi(heterocyclic) compounds are formally the addition product of a saturated NHC and the alcohol group of the N-functionalised arm. Using these compounds, the synthesis and structural characterisation of the first electropositive metal complexes of saturated N-heterocyclic carbenes has been achieved, and examples structurally characterised for the yttrium(III) and the uranyl [UO(2)](2+) cations.

Dedicated to Professor Jean-Claude Bünzli on the occasion of his 65th birthday were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL 4 ], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation-state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL 4 ].