Selective Si-C(sp3) bond cleavage of a silyl-bridged amido alkyl ligand in an yttrium complex.

Compared with Si-C(sp2 and sp) bonds bearing neighboring π-bond hyperconjugative interactions, the activation of robust Si-C(sp3) bonds has proved to be a challenge. Herein, two distinct Si-C(sp3) bond cleavages have been realized by rare-earth-mediated and nucleophilic addition of unsaturated substrates. The reactions of TpMe2Y[κ2-(C,N)-CH(SiH2Ph)SiMe2NSiMe3](THF) (1) with CO or CS2 gave two endocyclic Si-C bond cleavage products, TpMe2Y[κ2-(O,N)-OCCH(SiH2Ph)SiMe2NSiMe3](THF) (2) and TpMe2Y[κ2-(S,N)-SSiMe2NSiMe3](THF) (3), respectively. However, 1 reacted with nitriles such as PhCN and p-R'C6H4CH2CN in a 1 : 1 molar ratio to yield the exocyclic Si-C bond products TpMe2Y[κ2-(N,N)-N(SiH2Ph)C(R)CHSiMe2NSiMe3](THF) (R = Ph (4); R = C6H5CH2 (6H); R = p-F-C6H4CH2 (6F); and R = p-MeO-C6H4CH2 (6MeO)), respectively. Moreover, complex 4 can continuously react with an excess of PhCN to form a TpMe2-supported yttrium complex with a novel pendant silylamido-substituted ß-diketiminato ligand, TpMe2Y[κ3-(N,N,N)-N(SiH2Ph)C(Ph)CHC(Ph)N-SiMe2NSiMe3](PhCN) (5).

Lanthanide-catalyzed deamidative cyclization of secondary amides and ynones through tandem C-H and C-N activation.

The tandem inert α-C-H and C-N bond activation of amides represents a highly valuable but challenging transformation in organic synthesis. Herein, a simple rare earth metal amido complex has been shown to catalyse unprecedented cyclization of amides with ynones to form trisubstituted 2-pyrones. This protocol significantly enables the selective merger of inert α-C-H and C-N bond activations of amides and indicates a particular role of rare earth catalysts in enhancing the selectivity for the α-C-H bond of amides in the presence of N-H bonds.

Cooperative Rare-Earth/Lithium-Mediated Conversion of White Phosphorus.

The rare-earth/lithium cooperative effect on functionalization of white phosphorus has been investigated. The reaction of diazabutadiene-supported yttrium hydride chelated a LiPPh2 molecule (LY ⋅ THF)2 (µ-H)2 [µ-PPh2 (Li)] (1, L=N,N'-di(2,6-diisopropylphenyl)-1,4-diazabutadiene) with P4 gave two novel mixed Y/Li multinuclear polyphosphorus complexes (LY ⋅ THF)2 [cyclo-P3 ]Li(THF)3 (2) and [Li(THF)4 ]+ [(LY ⋅ THF)3 (norborane-P7 )Li(THF)]- (3), accompanied with the elimination of diphosphorus compound Ph2 PPPh2 (4) and H2 . However, the comparative reaction of yttrium hydride (LY ⋅ THF)2 (µ-H)2 with P4 afforded a trinuclear yttrium pyramid-P4 complex (LY ⋅ THF)3 (µ3 -P(PH)3 ) (5). Further investigations show that 5 cannot continuously react with LiPPh2 to form 2 and 3, and LiPPh2 reacted with P4 to form a Zintl-P7 lithium complex (TMEDA⋅Li)3 (Zintl-P7 ) (6) and 4. These results indicated that the cooperation of Y/Li for activation of P4 is a key for the formation of 2 and 3. All new compounds have been characterized by NMR spectroscopy and single-crystal X-ray diffraction studies.

La-Catalyzed Decarbonylation of Formamides and Its Applications.

Herein we report the first catalytic decarbonylation and decarbonylative hydroamination of formamides without using additives enabled by a redox-neutral rare earth catalyst. The protocol displays complete N-aryl/alkenyl formamide-selectivity, thus providing a wide variety of creative uses of the N-formylation and N-deformylation method and opening up new prospects for minimizing waste and controlling the required selectivity in amine transformation events.

Sequential Addition of Amines to Nitrile and Carbon-Carbon Multiple Bond: A Route to 7-Amino-5H-dibenzo[c,e]azepines.

A rare earth metal-catalyzed sequential inter- and intramolecular C-N bond formation of 2-nitrile-2'-alkenyl(alkynyl)biphenyls with amines has been developed, which provides a straightforward and efficient access to a range of new functional dibenzo[c,e]azepines. This represents the first examples of direct construction of seven-membered azaheterocycle from unsaturated nitriles and amines. Such transformations have the advantages of avoiding the use of additives, easily available starting materials, step- and high atom-economy, mild reaction conditions, and high selectivity.

Modification of Yttrium Silyl-Bridged Amide Alkyl Complexes through Si-H/C-H Cross-Dehydrocoupling of Silanes with a Silylamino Ligand: Synthesis, Reactivity, and Mechanism.

A new method for the modification of a silylamino ligand has been developed through mono and dual C(sp3 )-H/Si-H cross-dehydrocoupling with silanes. The reaction of [LY{η2 -(C,N)-CH2 Si(Me2 )NSiMe3 }] (L=bis(2,6-diisopropylphenyl)-ß-diketiminato, L' (1L '); L=tris(3,5-dimethylpyrazolyl)borate, TpMe2 (1TpMe2 )) with 2 equivalents of PhSiH3 in toluene gave the complexes [LY{η2 -(C,N)-C(SiH2 Ph)2 Si(Me2 )NSiMe3 }] (L=L' (2L' ); L=TpMe2 (2TpMe2 )). Moreover, 1TpMe2 reacted with the secondary silanes Ph2 SiH2 and Et2 SiH2 to afford the corresponding mono C-H activation products [TpMe2 Y{η2 -(C,N)-CH(SiHR2 )Si(Me2 )NSiMe3 }] (R=Ph (4 b); R=Et (4 c)). The equimolar reaction of 1TpMe2 with PhSiH3 also produced the mono C-H activation product 4 a ([TpMe2 Y{η2 -(C,N)-CH(SiH2 Ph)Si(Me2 )NSiMe3 }(thf)]). A study of their reactivity showed that4 a facilely reacted with 2 equivalents of benzothiazole by an unusual 1,1-addition of the C=N bond of the benzothiazolyl unit to the Si-H bond to give the C-H/Si-H cross-dehydrocoupling product [(TpMe2 )Y{η3 -(N,N,N)-N(SiMe3 )SiMe2 CH2 Si(Ph)(CSC6 H4 N)(CHSC6 H4 N)}] (5). These results indicate that this modification endows the silylamino ligand with novel reactivity.

An Yttrium Organic cyclo-P4 Complex and Its Selective Conversions.

The rare-earth-metal organic cyclo-P4 complex (LY·DMAP)2[1,2-R2- cyclo-P4] (2, L = N, N'-2,6-diisopropylphenyl-1,4-diazabutadiene, DMAP = 4- N, N'-dimethylpyridine, R = CH2C6H4NMe2-2) was synthesized by direct functionalization of P4 using the rare-earth-metal alkyl complex LYR(THF) (1) for the first time. Further investigations indicated that three selective conversions of the cyclo-P4 species have been realized by alkyl migration. Complex 2 was slowly transformed into a R2P-substituted cyclo-P3 cluster (LY·DMAP)2[ cyclo-P3PR2] (3) under heating conditions. The reaction of 2 with 1 equiv of KR gave the unsubstituted cyclo-P3 complex (LY·THF)2[ cyclo-P3]K (4) in quantitative yield, accompanied by the elimination of the organophosphorus compound PR3 (5). Treatment of 2 with HMPA afforded the structurally characterized Zintl-type P7 complex (LY·HMPA)3P7 (6). The formation of complexes 3, 4, and 6 revealed that unusual alkyl migrations in the polyphosphorus complexes occurred in these reactions, and the transformations from cyclo-P4 into cyclo-P3 also provided a new insight into the stepwise degradation of P4 using metal complexes.

Oxidation and chalcogenylative disproportionation of anionic phosphide ligands in yttrium complexes with elemental sulfur and selenium.

The oxidation and disproportionation of anionic phosphide ligands in yttrium complexes with elemental sulfur and selenium are reported. The mixed TpMe2/Cp supported yttrium phosphide complex TpMe2CpYPPh2(THF) (1) reacted with one equiv. of elemental S or Se in THF at room temperature to deliver two structurally characterized yttrium dithio- or monoseleno-phosphinates TpMe2CpYS2PPh2(THF) (2) and TpMe2CpYSePPh2(THF) (4Se), respectively. Further investigations showed that the yttrium thiophosphinate TpMe2CpYSPPh2(THF) (4S) can be isolated from the reactions of 2 and 1 or 1 and elemental S in a short reaction time. Moreover, after keeping 4S or 4Se in THF solution for some days, 2 or [(TpMe2)2Y]+[Se2PPh2]- (5) was obtained by a disproportionation process. The mechanism for the construction of the Ph2PE- and Ph2PE2- (E = S, Se) ligands has been discussed based on the in situ NMR experiments and some designed reactions.

Living 3,4-(Co)Polymerization of Isoprene/Myrcene and One-Pot Synthesis of a Polyisoprene Blend Catalyzed by Binuclear Rare-Earth Metal Amidinate Complexes.

Mononuclear amidinate yttrium complex C4 H9 C(NR)2 Y(o-CH2 C6 H4 NMe2 )2 (R=2,6-iPr2 C6 H3 ) and a series of binuclear rare-earth metal complexes bearing a bridged amidinate ligand [(RN)2 C(CH2 )4 C(NR)2 ][RE{CH2 C6 H4 (o-NMe2 )}2 ]2 (R=2,6-iPr2 C6 H3 , RE=Y, Lu, Sc) were synthesized and fully characterized. The catalytic behavior of these complexes for (co)polymerization of conjugated dienes such as isoprene and myrcene in the presence of co-catalyst [Ph3 C][B(C6 F5 )4 ] was investigated. These catalytic systems show impressively high activity and 3,4-regioselectivity in living (co)polymerization. The binuclear bridged amidinate yttrium catalytic system not only exhibits the highest activity among the reported catalytic systems for 3,4-polymerization of isoprene but also allows the steady polymerization in a living manner from -20 to 80 °C. Compared with the dramatic drop of 3,4-selectivity for the mononuclear analogue, the binuclear catalytic system still shows moderate 3,4-selectivity at 80 °C. Moreover, a facile one-pot synthetic strategy for a polymer blend containing 3,4- and 1,4-polyisoprene (PIP) was established through the in situ modification of the active amidinate yttrium species by addition of an excess amount of AlMe3 .

Unprecedented Reaction Mode of Phosphorus in Phosphinidene Rare-Earth Complexes: A Joint Experimental-Theoretical Study.

Reactions of trinuclear rare-earth metal complexes bearing functionalized phosphinidene ligand [L3Ln3(µ2-Me)2(µ3-Me)(µ3-η1:η2:η2-PC6H4-o)] (L = [PhC(NC6H4iPr2-2,6)2]-, Ln = Y (1a), Lu (1b)) with phenylacetylene, CO2, diisopropyl carbodiimide, isocyanide, or PhSSPh lead to the formation of a series of phosphorus-containing products. The reaction of 1 with CS2 yields two novel P-methyl-phosphindole-2,3-dithiolate dianion complexes, revealing an unusual tandem desulfurization/coupling/cyclization reaction mode of CS2. A possible reaction pathway was determined by density functional theory calculations. This emphasizes the key role of the reduction power of the formal P2- part of the phosphinidene in the C-S bond cleavage.

Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare-Earth Complexes: Non-Redox Oxygen Atom Transfer.

The preferential substitution of oxo ligands over alkyl ones of rare-earth complexes is commonly considered as "impossible" due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare-earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln-oxo bond, but also protect the highly reactive Ln-alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non-redox rare-earth-mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare-earth oxo complexes.

Facile Construction of Yttrium Pentasulfides from Yttrium Alkyl Precursors: Synthesis, Mechanism, and Reactivity.

Treatment of the yttrium dialkyl complex TpMe2Y(CH2Ph)2(THF) (TpMe2 = tri(3,5 dimethylpyrazolyl)borate, THF = tetrahydrofuran) with S8 in a 1:1 molar ratio in THF at room temperature afforded a yttrium pentasulfide TpMe2Y(κ4-S5) (THF) (1) in 93% yield. The yttrium monoalkyl complex TpMe2CpYCH2Ph(THF) reacted with S8 in a 1:0.5 molar ratio under the same conditions to give another yttrium pentasulfide [(TpMe2)2Y]+[Cp2Y(κ4-S5)]- (10) in low yield. Further investigations indicated that the S52- anion facilely turned into the corresponding thioethers or organic disulfides, and released the redundant S8, when it reacted with some electrophilic reagents. The mechanism for the formation of the S52- ligand has been investigated by the controlling of the reaction stoichiometric ratios and the stepwise reactions.

Lanthanide-Catalyzed Reversible Alkynyl Exchange by Carbon-Carbon Single-Bond Cleavage Assisted by a Secondary Amino Group.

Lanthanide-catalyzed alkynyl exchange through C-C single-bond cleavage assisted by a secondary amino group is reported. A lanthanide amido complex is proposed as a key intermediate, which undergoes unprecedented reversible ß-alkynyl elimination followed by alkynyl exchange and imine reinsertion. The in situ homo- and cross-dimerization of the liberated alkyne can serve as an additional driving force to shift the metathesis equilibrium to completion. This reaction is formally complementary to conventional alkyne metathesis and allows the selective transformation of internal propargylamines into those bearing different substituents on the alkyne terminus in moderate to excellent yields under operationally simple reaction conditions.

Small molecule activation by mixed methyl/methylidene rare earth metal complexes.

Diverse reactivity patterns of mixed tetramethyl/methylidene rare-earth complexes bearing bulky benzamidinate coligands L3Ln3(µ2-Me)3(µ3-Me)(µ3-CH2) [L = [PhC(NC6H3(i)Pr2-2,6)2](-); Ln = Y(), Lu()] with PhCN, alkynes, and CS2 have been established. Reaction of complexes with PhCN gave the µ3-CH2 addition complexes (NCN(dipp))3Lu3(µ2-Me)3(µ3-Me)[µ-η(1):η(1):η(3)-CH2C(Ph)N] [Ln = Y(), Lu()]. Treatment of complexes with phenylacetylene afforded unexpected alkenyl dianion complexes L3Ln3(µ2-Me)3(µ3-Me)(µ-η(1):η(3)-PhC[double bond, length as m-dash]CMe) [Ln = Y(), Lu()] through the insertion of rare earth methylidene into a C-H bond in a reductive fashion. However, reaction of complexes and HC[triple bond, length as m-dash]CSiMe3 gave µ3-Me protonolysis complexes L3Ln3(µ2-Me)3(µ3-C[triple bond, length as m-dash]CSiMe3)(µ3-CH2) [Ln = Y (), Lu ()] in excellent yields. Treatment of complexes with CS2 led to the formation of the methyl activation complexes L3Ln3(µ2-Me)2(µ3-CH2)(µ3-η(1):η(2):η(2)-S2C[double bond, length as m-dash]CH2) [Ln = Y(), Lu()]. All the new complexes were fully characterized.

Cycloamidination of Aminoalkenes with Nitriles: Synthesis of Substituted 2-Imidazolines and Tetrahydropyrimidines.

The first catalytic cycloamidination of aminoalkenes with nitriles has been achieved by using rare-earth complexes. This reaction is equivalent to the desired intramolecular hydroamination of alkenylamidines, and allows a new direct access to substituted 2-imidazolines and tetrahydropyrimidines in high yields under operationally simple reaction conditions. Moreover, the methodology is also efficient for synthesis of symmetric and unsymmetric bridged diimidazolines. Compared with the traditional stepwise-mediated synthetic approaches, the present method avoids the use of additives and harsh reaction conditions, and thus leads to a completely different product distribution. Mechanistic data suggest that the reaction involves the initial NH activation by lanthanide complex followed by nitrile insertion into a Ln-N bond to form an amidinate lanthanide intermediate which undergoes the cyclization.

Ln[N(SiMe3 )2 ]3 -catalyzed cross-diinsertion of C≡N/C≡C into an N≡H bond: facile synthesis of 1,2,4-trisubstituted imidazoles from propargylamines and nitriles.

A lanthanide-catalyzed sequential insertion of CN and CC into an NH bond is presented. The convenient reaction, which proceeds under mild conditions, is an efficient method for preparing 1,2,4-trisubstituted imidazoles directly from readily available propargylamines and nitriles.

Reactivity of Tp(Me2) -supported yttrium alkyl complexes toward aromatic N-heterocycles: ring-opening or C-C bond formation directed by C-H activation.

Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon-carbon double bond through multiple C-H activation were observed in the reactions of Tp(Me2) -supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp(Me2) Y(µ-N,C-Im)(η(2) -N,C-Im)]6 (1; Im=1-methylimidazolyl) through two kinds of C-H activations at the C2- and C5-positions of the imidazole ring. However, [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C-C coupling/ring-opening/C-C coupling product [Tp(Me2) Y{η(3) -(N,N,N)-N(CH3 )C6 H4 NHCHC(Ph)CN(CH3 )C6 H4 NH}] (2). Further investigations indicated that [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C-C coupling/ring-opening product {(Tp(Me2) )Y[µ-η(2) :η(1) -SC6 H4 N(CHCHPh)](THF)}2 (3). Moreover, the mixed Tp(Me2) /Cp yttrium monoalkyl complex [(Tp(Me2) )CpYCH2 Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp(Me2) CpY(µ-N,C-Im)]3 (5), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp(Me2) Y(Im-Tp(Me2) )] (7; Im-Tp(Me2) =1-methyl-imidazolyl-Tp(Me2) ) and [Cp3 Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a CC bond through multiple C-H activations.

Homometallic rare-Earth metal phosphinidene clusters: synthesis and reactivity.

Two new trinuclear µ3 -bridged rare-earth metal phosphinidene complexes, [{L(Ln)(µ-Me)}3 (µ3 -Me)(µ3 -PPh)] (L=[PhC(NC6 H4 iPr2 -2,6)2 ](-) , Ln=Y (2 a), Lu (2 b)), were synthesized through methane elimination of the corresponding carbene precursors with phenylphosphine. Heating a toluene solution of 2 at 120 °C leads to an unprecedented ortho CH bond activation of the PhP ligand to form the bridged phosphinidene/phenyl complexes. Reactions of 2 with ketones, thione, or isothiocyanate show clear phospha-Wittig chemistry, giving the corresponding organic phosphinidenation products and oxide (sulfide) complexes. Reaction of 2 with CS2 leads to the formation of novel trinuclear rare-earth metal thione dianion clusters, for which a possible pathway was determined by DFT calculation.

Versatile Reactivity of Scorpionate-Anchored Yttrium-Dialkyl Complexes towards Unsaturated Substrates.

A series of unusual chemical-bond transformations were observed in the reactions of high active yttrium-dialkyl complexes with unsaturated small molecules. The reaction of scorpionate-anchored yttrium-dibenzyl complex [Tp(Me2)Y(CH2Ph)2(thf)] (1, Tp(Me2)=tri(3,5-dimethylpyrazolyl)borate) with phenyl isothiocyanate led to C=S bond cleavage to give a cubane-type yttrium-sulfur cluster, {Tp(Me2)Y(µ3-S)}4 (2), accompanied by the elimination of PhN-C(CH2Ph)2. However, compound 1 reacted with phenyl isocyanate to afford a C(sp(3)) H activation product, [Tp(Me2)Y(thf){µ-η(1):η(3)-OC(CHPh)NPh}{µ-η(3):η(2)-OC(CHPh)NPh}YTp(Me2)] (3). Moreover, compound 1 reacted with phenylacetonitrile at room temperature to produce γ-deprotonation product [(Tp(Me2))2Y](+)[Tp(Me2)Y(N=C=CHPh)3](-) (6), in which the newly formed N=C=CHPh ligands bound to the metal through the terminal nitrogen atoms. When this reaction was carried out in toluene at 120 °C, it gave a tandem γ-deprotonation/insertion/partial-Tp(Me2)-degradation product, [(Tp(Me2)Y)2(µ-Pz)2{µ-η(1):η(3)-NC(CH2Ph)CHPh}] (7, Pz=3,5-dimethylpyrazolyl).

Ln[N(SiMe3)2]3-catalyzed cycloaddition of terminal alkynes to azides leading to 1,5-disubstituted 1,2,3-triazoles: new mechanistic features.

The first example of rare earth metal-catalyzed cycloaddition of terminal alkynes to azides resulting in the formation of 1,5-disubstituted 1,2,3-triazoles is described. Preliminary studies revealed that the present cycloaddition shows unprecedented mechanistic features involving a tandem anionic cascade cyclization and anti-addition across the C≡C triple bond.