Using the nucleophilicity of NHCs and aNHCs, as well as the leaving group ability of the former, the carbon-carbon double bond of imidazol-2-ylidenes can be readily mono- and di-functionalized. These results provide also a new light on the formation of abnormal carbene adducts from classical unsaturated NHCs.
A series of calix[5]arene bismuth(III) and antimony(III) mono- and bimetallic complexes were synthesized and fully characterized by NMR, X-ray, IR, mp, UV-Vis and elemental analysis. Reaction of p-tert-butylcalix[5]arene (tBuC5(H)5) trianionic salts M'3.tBuC5(H)2 (M'=Li, Na, K) with MCl3 (M=Bi, Sb) yielded monometallic complexes [Bi{tBuC5(H)2}] 1 and [Sb{tBuC5(H)2}] 2, respectively. 1H NMR spectra of both complexes showed two remaining OH groups available for further reactivity. Alternatively, complexes 1 and 2 can be obtained by reacting tBuC5(H)5 in a 1:1 ratio with M(OtBu)3, but the yields are lower. When the tBuC5(H)5 lower rim monobenzyl ether [tBuC5(Bn)(H)4] is treated in a 1:1 ratio with Bi(OtBu)3, the monometallic complex [Bi{tBuC5(Bn)(H)}]2 3 is prepared. If, however, [tBuC5(Bn)(H)4] reacts with Sb(NMe2)3 or Sb(OtBu)3 in a 1:2 ratio the production of the bimetallic complex [Sb2O{tBuC5(Bn)}] 4 is observed. p-Benzylcalix[5]arene (BnC5(H)5) reacts with excess Bi(OtBu)3 to produce the bimetallic complex [Bi2O{BnC5(H)}]2 5. 1H NMR spectra of 5 display patterns characteristic for a cone conformer in solution. Treatment of calix[5]arene [HC5(H)5] with one equivalent of Bi[N(SiMe3)2]3 or with 0.75 equivalents of Sb(NMe2)3 yields bimetallic complexes [Bi2O{HC5(H)}] 6 and [Sb2O{HC5(H)}] 7, respectively. The reactivity of monometallic complexes 1 and 2 was tested in order to investigate the availability of their remaining OH groups. Treatment of 1 with Bi(OtBu)3 at ambient temperature yields bimetallic complex [Bi2O{tBuC5(H)}]2 8 while the reaction of complex 2 with Sb(OtBu)3 in a 1:1 ratio produces complex [Sb2O{tBuC5(H)}] 9. The crystal structures of the monometallic bismuth complexes 1 and 3 display dimeric units with the calixarene ligands in distorted cone and "paco-in" conformations, respectively. Complexes 4, 7 and 9 are all monomeric units, displaying [(RO)2Sb]2(micro-O) cores and the calixarene ligands in 1,2-alternate conformation. The dimeric units of bimetallic complexes 5 and 8 contain Bi4O2(OR)8 core structures that force the calixarene ligands to adopt a flattened cone conformation.
The synthesis and full characterization (mp, NMR, UV/vis, FTIR, and elemental analysis) of 13 bismuth aryloxides are reported. We have prepared bismuth aryloxides with alkyl, aryl, and allylic substituents on the aryl rings. Eleven of these bismuth aryloxides have been characterized with single crystal X-ray diffraction methods. Bismuth-donor interactions (donor = aryl, methoxy) are observed in several cases. Three unexpected bismuth oxo aryloxides (6c, 9c, 11c) were also isolated. Complex C(77)H(102)Bi(4)Br(6)O(8) (6c) results from apparent C-H activation and Bi-C bond formation as a sideproduct in the synthesis of Bi(O-2,6-(i)Pr(2)-4-BrC(6)H(2))(3) (6). Cluster 9c has a Bi(32)O(56) core, and cluster C(90)H(90)Bi(4)Li(2)O(12) (11c) is the second lithium bismuth oxo cluster reported to date.
The preparation and full characterization of a variety of mono-([L1-H]), di-([L2-H 2 ], [L2A-H2]), and tri-([L3-H 3 ]) 1,2,3-triazolium salts constructed form "clicked" hydroxybenzene derivatives are reported. Deprotonation with potassium hexamethyldisilazide, followed by in situ metalation, allowed for the synthesis of a series of mono-(L1•[M]), di-(L2•[M] 2 , L2•[M] 2 ), and trinuclear (L3•[M] 3 ) group 9−11 (M = [Rh(CO) 2 Cl], [Pd(allyl)Cl], and [AuCl]) triazol-5-ylidene metal complexes. In solution, all metal complexes feature symmetrical patterns displaying C 2 and C 3 fold axes when supported by di-and tritriazol-5-ylidene ligands. The vibration frequencies of Ln•[Rh(CO) 2 Cl] n (n = 1−3) complexes indicate that the electron-donor properties of the new ligands are comparable to those for previously reported MIC complexes and superior to classical NHCs. Prompting coordination of the vicinal phenoxy group to the metal centers proved unsuccessful after treatment of the Ln•[Rh(CO) 2 Cl] n and Ln•[Pd(allyl)Cl] n (n = 1−3) precursors with AgBF 4 ; the expected chelated cationic complexes were highly unstable, indicating a weak or no coordination availability through the oxygen atom. Crystal structures of the complexes L1•[AuI] and L2A•[Pd(allyl)I] 2 illustrated the metal center geometrical environment and confirmed the lack of coordination through the phenoxy moiety of the ligand. Preliminary catalytic trials established the enhanced performance of di-and trimetallic palladium complexes in cross-coupling reactions and the intramolecular cyclization of enynes catalyzed by gold complexes.
A series of calix[n]arene (n=6-8) bismuth and antimony complexes were synthesized and fully characterized by NMR, X-ray, IR, UV-Vis and elemental analysis. The monobismuth calix[6]arene complex [Bi{tBuC6(H)3}]2 1 was prepared by the reaction of para-tert-butylcalix[6]arene (tBuC6(H)6) with one equivalent of Bi[N(SiMe3)2]3. Complex 1 featured a Bi2(micro-O)2 central core similar to other bismuth calixarene complexes prepared by our group. Reaction of calix[6]arene (HC6(H)6) with two equivalents of Bi(OtBu)3 yielded different outcomes depending on the reaction solvent. If THF was used, complex [Bi{HC6(H)3}] 2 was obtained in 72% yield; however, when toluene was used, complexes 2 and [Bi2{HC6}] 3 were isolated in 23 and 57% yields, respectively. Mononuclear complexes 1 and 2 displayed dimeric structures in the solid state with cone-like conformations for the calixarene ligands. The 1H NMR spectrum of complex 2 displays patterns for an asymmetric structure with two signals in a 2:1 ratio for the unreacted OH groups. Treatment of calix[6]arenes RC6(H)6 (R=H, tBu) with two equivalents of SbR3 (R=OtBu, NMe2) produced dinuclear complexes [Sb2{HC6}] 4, and [Sb2{tBuC6}] 5, respectively. The 1H NMR spectra for the dinuclear complexes 3, 4, and 5 showed the characteristic calixarene pattern for a 1,2,3-alternate conformer. In the process of recrystallization of complex 4 an unexpected trimetallic complex with composition [Sb3O2{HC6(H)}] 4a was obtained in low yield. Treatment of para-tert-butylcalix[7]arene (tBuC7(H)7) with two equivalents of Bi(OtBu)3 produced the bimetallic complex [Bi2O{tBuC7(H)3}]2 6. Complex 6 contains an overall Bi4O2(OAr)8 core system with a structural resemblance to other bimetallic bismuth calixarene complexes reported by our group. The larger para-benzylcalix[8]arene (BnC8(H)8) and calix[8]arene (HC8(H)8) reacted with excess Bi(OtBu)3 to produce the tetranuclear complexes [Bi4O2{HC8}] 7 and [Bi4O2{BnC8}] 8, respectively. The solid state structure of complex 8 featured a dimeric unit with the calixarene ligands in pinched-cone conformation and displaying an overall Bi8O4(OAr)16.H2O core. No metal pi-arene interactions were observed.
A series of bimetallic complexes supported by a 4-phosphino substituted NHC ligand have been synthesized. The use of the stable ligand reduces the number of synthetic steps and allows for a wide range of metal combinations.
Following a copper catalyzed alkyne azide cycloaddition (CuAAC) and N-alkylation protocols, we report the preparation of a hybrid N-heterocyclic/mesoionic [NHC(H)-MIC(H)][2I] salt (1) in high yields. The treatment of salt 1 with CuO and KI yields a second hybrid NHC/MIC proligand featuring a tetraiodocuprate anion [NHC(H)-MIC(H)][CuI] (2). Through selective deprotonation and metalation, both salts 1 and 2 can generate either the chelate heterodicarbene complexes (3) with the rare [NHC·(M)·MIC][MX] general formula (M = Pd, Rh) or NHC-anchored/pendent triazolium species (4) [NHC·(M)-MIC(H)]. If the triazolium moiety of type 4 complexes is deprotonated with KHMDS in the presence of a second metal center, a series of heterobimetallic complexes of the type [NHC·(M)-MIC·(M')] (5) are achieved. Interestingly, the reaction of salt 2 with KHMDS yields the bimetallic copper heterodicarbene (6) which can be a useful transfer reagent for the preparation of type 3 complexes. A variety of synthetic routes for the preparation of complexes 3-5 and their full characterization in solution and in the solid state will be discussed.
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