Three Pyrazole Boron Rare-earth Alkyl Compounds Synthesis And Reactions

It is a long-standing research subject in organolanthanide chemistry that novel rare-earth organometallic complexes with unique reactivity and efficient catalytic activity are synthesized and applied in the field of organic synthesis and polymerization of olefins. Many efforts focus on the search of novel supporting ligands to alternate the well-defined cyclopentadienyl systems. The polypyrazolyborate ligands (Tp*) represent an attractive and versatile alternative due to the fine-tuning of the ligand size and controlling the metal coordination sphere through the modification of the3-and5-substituents of the pyrazolyl rings. As the extension of the synthesis and reactivity of Tp*-supported rare earth organometallic complexes, this paper focus on investigating the synthesis and reactivity of TpMe2-supported rare-earth monoalkyl, dialkyl and silyl amide complexes. Herein we have synthesized77new compounds, among the structures of72were determined by X-ray single-crystal diffraction analysis. The main results are as follows:1. We have synthesized successfully TpMe2/Cp mixed monoalkyl complex (TpMe2)CpYCH2Ph(THF)(2-1) by the introduction of the cyclopentadienyl ligand, avoided effectively the TpMe2ligand-degradation. Protonolysis of2-1with acid organic reagent such as phenylacetylene and o-aminopyridine gave the corresponding alkynyl and amide derivatives (TpMe2)CpYCCPh(THF)(2-2) and (TpMe2)CpY(η2-NH-Py)(2-3). It has been found that2-lcan react with a series of unsaturated substrates such as carbodiimides, isocyanate, isothiocyanate, and CS2under mild condition to form smoothly complexes (TpMe2)CpY[(RN)2CCH2Ph](R=*Pr(2-4a), Cy(2-4b),2,6-’Pr-C6H3(2-4c)),(TpMe2)CpY[XC(CH2Ph)NPh](X=S (2-5), X=O (2-6)) and (TpMe2)CpY[S2C(CH2Ph)](2-7). Moreover, we also investigated the reactions of2-1with benzyl azide, the product (TpMe2)CpY[η3-N(CH2Ph)N N(CH2Ph))(2-8) with η3coordination mode was achieved. Carbodiimides and isothiocyanate can also insert into the Y-C(alkynyl) σ-bond of2-2to yield complexes (TpMe2)CpY[(RN)2CC=CPh](R=’Pr(2-9a), Cy(2-9b)), and (TpMe2)CpY[SC(C=CPh)NPh](2-11). Further investigations indicated that2-1can catalyze effectively the cross-coupling reactions of phenylacetylene with carbodiimides in high yield to give N,N’-disubstituted propiolamidines (RN=C(C=CR’)(NHR))(R=’Pr (2-10a), Cy(2-10b)). However, it is not successful to attempt the hydroamination/cyclization of o-allylaniline catalyzed by2-1, we only obtained the benzyl abstraction product (TpMe2)CpY(NHC6H4CH2CH=CH2-o)(THF)(2-13). We also explored the reactivity of2-3toward some unsaturated substrates such as carbodiimides, isocyanate, and isothiocyanate. These results indicated that carbodiimides readily insert into the N-H bond of2-3to produce (TpMe2)CpY{η2-N[C(NR)(NHR)Py]}(R=iPr(2-14a), R=Cy(2-14b)). Similarly, the insertion and/or partially Cp-abstracted products (TpMe2)[η2-OC(NPh)-NHPy]Y[η-η2:η2-N(Ph)C(O)NPy]YCp(TpMe2)(2-15) and (TpMe2) CpY[η2-N(Ph)C-(NHPy)S](2-16), were obtained in the reactions of2-3with phenyl isocyanate and phenyl isothiocyanate, respectively. We also found that2-16can react with2-5to form a dinuclear complex (TpMe2)[η2-N(Ph)C(CH2Ph)S]Y[μ-η2:η2-N(Ph)C(S)NPy]-YCp(TpMe2)(2-17). These results were significantly different from those observations of the reactions of Cp2Ln(η2-NHPy) with these molecules.2. Treatment of TpMe2YCl2(THF) with two equiv of KCH2Ph in THF gave the expected dialkyl complex TpMe2Y(CH2Ph)2(THF)(3-1) in high yield. The reactions of3-1with PhNCS and PhNCO led to the formation of a novel cubane-type sulfur complex [TpMe2Y(3-S)]4(3-2) and an insertion and hydrogen-abstracted product TpMe2Y(THF)[μ-η1:η3-OC(CHPh)NPh][μ-η3:η2-OC(CHPh)NPh]YTpMe2(3-3) in moderate yields, respectively.3-3can further react with (CH=3)3SiCl to give a1,4-addition product (TpMe2)YCl{η2-N(Ph)C[CPh(SiMe3)]O}(THF)(3-4). The investigations on the reactivity of3-1toward PhCH2CN indicated that the products depend on the reaction conditions. For example, the reaction of3-1with PhCH2CN in THF at room temperature to form [(TpMe2)Y]+[TpMe2Y(NCCHPh)3]-(3-5), but this reaction in toluene at120℃to give TpMe2Y[μ--η1:η1-Pyrazoyl]2[μ-η1:η2-NC (CH2Ph)CHPh]YTpMe2(3-6). In contrast to the above observations, the reaction of3-1with carbodiimides only afforded the simple Y-C σ-bond insertion products TpMe2Y(CH2Ph)[(RN)2C(CH2Ph)](R=iPr (3-8a); R=Ar=C6H3-iPr-2,6(3-8b)). The reaction of3-1with2,6-diisopropylaniline did not give the expected rare-earth terminal imido complex TpMe2Y=NAr, only was isolated a benzyl-abstracted product TpMe2Y(NHAr)CH2Ph(THF)(3-9). Interestingly,3-9reacted with one equiv of DIC to produce a symmetric dianionic guanidinate complex Tp e Y[(’PrN)2C=NAr](3-10). To give an insight of the mechanism for the formation of3-10, the reaction of3-8a with one equiv of2,6-diisopropylaniline at room temperature was investigated. Nevertheless, the reaction, even heated at higer mperature in toluene for a long time, only afforded complex TpMe2Y(NHAr)[(iPrN)2C(CH2Ph)](3-11). It should be noted that the reaction of3-1with o-aminopyridine generated a bridged-imine product TpMe2(THF)Y(μ-η1:η2-NPy)YTpMe2(3-12), different from those observed in the reaction of3-1with2,6-diisopropylaniline.3. The TpMe2-supported yttrium alkyl complexes2-1and3-1displayed unique reactivity toward some aromatic N-heterocycles. Treatment of2-1with two equiv of1-methylbenzimidazole to give a C-H activation product (TpMe2)CpY[η2-(N3,C2)-N C7H4NCH3](NC7H5NCH3)(4-1).2-1reacted with one or two equiv of1-methylimidazole at room temperature to give a trinuclear metallomacrocyclic complex [(TpMe2)CpY(μ-η1:η1-(N3,C5)NC3H2NCH3)]3(4-2), in which the C-H bond at5-postion in imidazolyl ring was activated.2-1reacted with two equiv of1-methylimidazole at60℃to give two structural characterized products (TpMe2)Y{κ4-(N,N,N,N)-[NC(CH3)CHC(CH3)N]2BH[NC(CH3)CHC(N)CHCN(CH3) CHCHN]}(4-3) and Cp3Y(NC3H3NCH3)(4-4). The formation of4-3might undergo a N-heterocyclic carbene intermediate. Similarly, the reaction of3-1with two equiv of1-methylimidazole to form a hexnuclear metallomacrocyclic complex{(TpMe2)Y-[(μ-η1:η1-(N3,C5)NC3H2NCH3)][η72-(N3,C2)-NC3H2NCH3)]}6(4-5), in which two C-H bonds at2-or5-postion in imidazolyl ring were activated. However,3-1reacted with two equiv of1-methylbenzimidazole to afford (TpMe2)Y[η3-(N,N,N)-N(CH3)C6H4NCHCH(Ph)CHN(CH3)C6H4N](4-6), undergoing the C-H activation, carbon-carbon coupling, and ring-opening processes. To testify this, we also investigated the reaction of3-1with benzothiazole, and isolated an expected complex {(TpMe2)Y[μ-η2:η1-SC6H4N(CH=CHPh)](THF)}2(4-8). Further investigations indicated that the formation of4-8is independent of the reaction stoichiometry.4. We also investigated the reaction of2-1with organonitriles, isocyanide, and imine, and revealed some unusual transformations of these small molecules.2-1reacted with one equiv of benzonitrile to afford (TpMe2)CpY[NCPh(CH2Ph)](THF)(5-1) by a insertion of cyano group into Y-C σ-bond in12%yield, and its imine-enamine tautomer (TpMe2)CpY[NHCPh(CHPh)](THF)(5-2) in64%yield. It should be noted that this reaction was worked at80℃, and afforded5-1as major product. To further study the difference of reactivity of5-1and5-2, we also investigated their reactions with PhCN, and found that both of5-1and5-2cannot react with PhCN at room temperature, but5-2can react with PhCN in toluene at120℃to give the N-H bond addition product (TpMe2)CpY(N(H)C(Ph)NC=CH(CH2Ph)Ph)(5-3)(21%), companied with the formation of5-1(49%)(Scheme2).5-3cannot further react with excess of PhCN though5also contains an active N-H bond similar to that of5-2.2-1reacted with one equiv of diphenyl maleimide at room temperature to result in the formation of the expected product (TpMe2)CpY[N(Ph)C(Ph)CH2Ph](5-4). To extend the scope of these reactions, we also investigated the reaction of2-1with tBuCN, and isolated(TpMe2)CpY[NC(’Bu)(CH2Ph)](THF)(5-5), a analogue of5-1. An equimolar reaction of2-1with2-NH2C6H4CN in THF at room temperature formed the benzyl protonation product [(TpMe2)CpY(μ-NHC6H4CN)]2(5-6) in24%isolated yield.5-6was also achieved in85℃through the same raction. The monomer product (TpMe2)CpY(NHC6H4CN)(HMPA)(5-7) can be obtained through the coordination of HMPA with5-6at room temperature. The reaction of5-6with2-1at room temperature gave the expected cyano group insertion product [(TpMe2)CpY (THF)]2(μ-NHC6H4C(CH2Ph)=N)(5-8). However, this reaction under the heating conditions gave an unexpected rearrangement product (TpMe2)CpY(THF)(η2-NH C6H4C(CH2Ph)=NH)(5-9) in lower yield, companied with the formation of small amount of (TpMe2)CpY (η2-Pyrazoyl-3,5-dimethyl)(5-10). Treatment of2-1with two equiv of o-aminobenzonitrile afforded a nucleophilic addition/cyclization product TpMe2Y[κ3-(4-NH(C8N2H4)(2-NHC6H4)](HMPA)(5-11).3-1reacted with one equiv of o-aminobenzonitrile to form a dianionic imido complex {TpMe2Y[μ-η1:η1-NHC6H4C(CH2Ph)N-o]}(5-12). The reaction of3-1with two equivof tBuNC at110℃to give a carbon-carbon coupling product TpMe2Y{η2-[N(tBu)C(CH2Ph)]2}(THF)(5-13).5. Four novel TpMe-supported yttrium phosphides and oxidephosphides complexes (TpMe2)CpYPPh2(THF)(6-1),(TpMe2)CpYOPPh2(THF)(6-2), TpMe2Y(PPh2)2(THF)(6-3), and [(TpMe2)2Y]+[TpMe2Y(OPPh2)3]-(6-4) were synthesized through the protonlysis of2-1and3-1with HPPh2or HP(O)Ph2. Treatment of6-1with1equiv of PhNCO/PhNCS at room temperature results in mono-insertion of PhNCO/PhNCS into the Y-P σ-bond of6-1to yield complex (TpMe2)CpY[OC(PPh2)NPh](THF)(6-5) or (TpMe2)CpY[SC(PPh2)NPh](6-6). While the reaction of6-1with2equiv of PhNCO afforded the diinsertion product (TpMe2)CpY[OC(PPh2)N(Ph)C(O)NPh](6-7). However,6-6cannot further react with PhNCS under the same conditions. Moreover,6-1can catalyze effectively the cyclotrimerization of PhNCO under mild conditions, but does not catalyze cyclotrimerization of PhNCS. We also investigated the reaction of these yttrium phosphides and oxidephosphides complexes with elemental sulfur (selenium, tellurium). Both of6-1and6-3reacts with one or two equiv of elemental sulfur (selenium, tellurium) to produce the rearrangement products [(TpMe2)2Y]+[X2PPh2]-(X=S(6-9a), X=Se(6-9b), X=Te(6-9c)). However, the reaction of6-2with one equiv elemental sulfur (selenium, tellurium) gave the expected complex (TpMe2)CpY[OP(X)PPh2](THF)(X=S(6-12a), X=Se(6-12b), X=Te(6-12c)).6. Rare-earth metal mediated C-Si cleavage and double C-H functionalizations of anionic N(SiMe3)2were observed for the first time, and offered a straightforward route to construct the anionic methyl-amidinate and single-carbon bridged bis-amidinate ligands. Treatment of TpMe2LnCl2(THF) with two equiv of K[(RN)2CN(SiMe3)2] gave the unexpected methylamidinate complexes TpMe2Ln[(RN)2CMe][N(SiMe3)3](R=isopropyl, Ln=Y (7-la), Er (7-lb); R=cyclohexyl, Ln=Y (7-2)) in moderate yields, which might undergo a Me-Si cleavage and carbodiimide-insertion process. Further investigations indicated that these complexes could be also synthesized by the stepwise reaction of Tp e2LnCl2with one equiv of the corresponding KGua and one equiv of KGua or KN(SiMe3)2. It should be noted that the reaction of TpMe2YCl2(THF) with one equiv of KGua yielded TpMe2Y(Cl)N(SiMe3)2(THF)(7-4), a C-N cleavage product. The formation of7-4indicated that this guanidinate ligand is not stable in the metal complexes with the TpMe2ligand, and takes place facilely a carbodiimide deinsertion. The reaction of TpMe2LnCl2with KGua(’Pr) and KN(SiMe3)2in a1:1:1ratio also afforded7-1, companied with the formation of small amount of y-methyl deprotonation product TpMe2Ln[(iPrN)2CCH2SiMe2NSiMe3)](Ln=Y (7-5a), Er (7-5b). TpMe2LnCl2(THF) reacted with two equiv of KN(SiMe3)2for1h (a short time), then subsequently with one equiv of CyN=C=NCy to afford the cocrystaline complexes ({TpMe2Ln[(CyN)2CMe][N(SiMe3)3]}{TpMe2Ln[(CyN)2CCH2SiMe2NSi-Me3)]}(Ln=Y(7-6a), Er(7-6b)). The single C-H functionallization product TpMe2Y[(CyN)2CCH2SiMe2NSiMe3)](7-7) has been obtained by the reaction TpMe2YCl2with two equiv of KN(SiMe3)2for12h, and subsequently with one equiv of DCC. It is also found that the double C-H functionalization product TpMe2Y{Me3SiNSi(Me2)CH[C(NiPr)2]2}K(THF)2(7-8) was isolated form the reaction of7-5a with one equiv of KN(SiMe3)2, subsequent with one equiv of’PrN=C=N’Pr or7-5a with one equiv of KGua(DIC).