Studies On Reaction Chemistry Of Lewis Pairs Based On Compounds Containing Silicon Or Germanium Element

Organosilicon and organogermanium chemistry is becoming a significantly important frontier research area in the main group chemistry.However,there are still lots of challenges with respect to the synthetic chemistry as well as the reaction chemistry of the silicon or germanium compounds having low oxidation states.The low oxidation state silicon or germanium compounds often have the small HOMO-LUMO energy gap and are highly reactive.Therefore,effective and even unconventional methods should be adopted for preparing such species,as has been a hot topic of current research.In recent years,the frustrated Lewis pair(FLP)chemistry has been intensively studied,where the key components of the FLP are involved in the low-valence main group element complexes.In view of these research backgrounds,this dissertation focuses on studies on the synthesis and reaction chemistry of low-valent silicon and germanium compounds.In the course of studying the FLP chemistry,the synthesis and reaction chemistry of the organoaluminum compounds were also investigated.Six sections work have been carried out in this paper and are outlined as follows.1.Study on reaction chemistry between amidinate silylene and alane and the mechanism thereof.A silicon-aluminum heterocycle LAl(SiH2SiH2)2AlL(L=PhC(NtBu)2)(2-1)was prepared from reaction of LSi-SiL(L=PhC(NtBu)2)and AlH3·NMe3.This is the first Al2Si4-heterocyclic compound so far as reported.Compound 2-1 exhibits a unique(N2Al)2(SiH2)4 centrosymmetric six-membered ring structure with a chair conformation,which is comparable with that of cyclohexane.Furthermore,two intermediate analogues,silylene-alane adduct LSi(AlMe3)-Si(AlMe3)L(2-2)and silylene-alane oxidative product[LAlHSiH2Mes]2(2-3)were obtained from the respective reactions of LSi-SiL and AlMe3 and of L(Mes)Si:and AlH3·NMe3.Compound 2-3 has an interesting arrangement of an Al-H and a SiH2 unit,which are in close vicinity to each other.2-3 might be important to function as a catalyst,due to the already activated bridging Al-H bonds.Compounds 2-1-2-3 have all been characterized by NMR,IR spectrum and X-ray sinlge-crystal diffraction.The reaction mechanism was also studied by the DFT calculations.2.Study on reaction chemistry between amidinate silylene and boron dihalidesA novel method has been developed for preparing the boryltrichlorosilanes by the oxidative addition reaction using the organoboron dihalides with the amidinate silylene.This is an unconventional route reported.L(Cl)Si:(L=PhC(N/Bu)2)reacted with PhBCl2 by insertion into the B-Cl bond followed with migration of L and Cl to give LBPhSiCl3(3-1).In a similar way,L(Cl)Si:reacted with RBCl2 to produce LBRSiCl3(R?2,4,6-Me3C6H2(Mes)(3-2);N(SiMe3)2(3-3)).Furthermore,L(Mes)Si:reacted with MesBBr2 to form compound LB(Mes)SiBr2Mes(3-4),however,L(NiPr2)Si:with MesBBr2 to LSiBr(N(iPr)2)(BBrMes)(3-5),where the later occurred by the oxidative addition reaction.Compounds 3-1-3-5 have all been characterized by NMR spectroscopy,of which compounds 3-2 and 3-4 were further confirmed by X-ray crystallography.These studies revealed a great influence by either the electronic or the steric property of the substituents at Si? center of the silylene species.3.Synthesis and reaction chemistry of the Ge?/B FLPsThe Lewis acidic B(C6F5)2 group was introduced to form intramolecular Ge?/B FLPs,and the reaction chemistry of the Ge?/B FLPs was studied toward organic multiple bond molecules.Firstly,amidinate ligand stabilized alkynyl Ge? compounds LGe(CCPh)(L?RC(NR')2,R=tBu,R'?Cy(4-1);R=tBu,R'?iPr(4-2);R?tBu,R'=2,6-iPr2C6H3(4-3);R=Ph,R'=tBu(4-4))were prepared,which reacted with B(C6F5)3 by 1,1-carboboration to give villyl-bridged Ge?/B FLP compounds LGe(Ph)C=C(C6F5)B(C6F5)2(L?RC(NR')2,R?tBu,R'?Cy(4-5);R?tBu,R'?iPr(4-6);R=tBu,R'?2,6-iPr2C6H3(4-7);R?Ph,R'?/Bu(4-8)).Secondly,the reactions using 4-5 with several carbonyl substrates were investigated.Compound 4-5 clicked the C=O bond of ketones to generate the C3GeB0-heterocycles[LGe(Ph)C=C(C6F5)B(C6F5)2](R1R2C-O)(R1=p-MeC6H4,R2=Me(4-9);R1R2=Ph(Et)C=(4-10)).However,it reacted with 1,2-diphenylethanedione to give[LGe(OCPh)2)(Ph)C=C(C6F5)B(C6F5)2](4-11)as a result by the oxidative addition reaction.Furthermore,4-5 clicked the C=N bond of nitriles to form the C3GeBN-heterocycles[(LGe)(Ph)C=C(C6F5)(B(C6F5)2)](ArC=N)(Ar?p-BrC6H4(4-12);Ar=(p-CF3)C6H4(4-13)).Finally,4-5 reacted with[(COD)RhCl]2 to yield complex[LGe(Ph)C=C(C6F5)B(C6F5)2]((COD)Rh-Cl)(4-14),showing a Ge?/B dipolar 1,2-cycloaddition charater caross the Rh-Cl bond.In comparison,4-5 reacted with AdN3 by the 1,1-additon way to produce[(LGe)(Ph)C=C(C6F5)(B(C6,F5)2)](NN2Ad)(4-15)?In addition,both the Ge"/B FLP 4-5 and 4-8 were able to react by the F atom migration reaction upon heat treatment to afford compounds[(LGe)(Ph)C=C(C6F5)(C6F4)(BF(C6F5))](L=/BuC(NCy)2(4-16);L?PhC(NtBu)2(4-17)).All of compounds 4-1-4-16 have been characterized by the NMRspectroscopy as well as by X-ray crystallography except for 4-3.These studies clearly revealed the high reactivity of the Ge?/B FLPs.4.The deoxygenation reaction chemistry by the intramolecular Ge?/B FLP,The reactivity of Ge?/B Lewis pairs towards carbonyl compound were further studied,which was involved by the oxidation state change of the Ge? in 4-5.Compound 4-5 reacted with iPrNCO by cleaving the C=O double bond followed with insertions of the O and iPrNC moieties separately into the Ge?B bond to yield a C2GeBO-heterocycle[LGe(Ph)OC(C6F5)B(C6F5)2](O)(5-1)and a C3GeB-heterocycle[LGe(Ph)OC(C6F5)B(C6F5)2](CNiPr)(5-2).Similar reaction models were observed for 4-5 with m-tolyl isocyanate and 4,4'-dphenylmethane diisocyanate,where two new C3GeB-heterocycles[LGe(Ph)C=C(C6Fs)B(C6F5)2)]?(CN(m-MeC6H4))(5-3)and {[(LG(Ph)C(C6F5)B(C6F5)2](CN(p-C6H4))?2CH2(54)were obtained,respectively.For the mechanistic study,reaction of 4-5 with tBuNC was also carried,giving[LGe(Ph)C=C(C6F5)B(C6F5)2](CN/Bu)(5-5),similar to 5-2.Meanwhile,reactions of 5-5 with ketones led to Ge-centered spiroheterocycles[(L*Ge)(Ph)C=C(C6F5)(B(C6F5)2)](O)(L*?tBuC(NCy)2(CRR'),R=p-MeOC6H4,R'=Me(5-6);R=C6H5CHCH,R'=Me(5-7);R?R'=Ph(5-8)),respectively.These reactions exhibited result by breakage of C=O bond followed with incorporation of the O atom into the Ge?B bond while of the(4-MeOC6H4)(Me)C moiety into the Ge-N bond.Both kinetic studies and theoretical calculations were performed to deeply understand the mechanism.5.Synthesis and reaction chemistry of the amino-bridged P/Si FLPs.Reactions of N-aryl(diphenylphosphanyl)aminosilane ArN(PPh2)SiMenCl3-n(Ar?2,4,6-Me3C6H2,n?0(6-la),1(6-2a),2(6-3a),3(6-4a);Ar?2,6-iPr2C6H3,n?0(6-lb),1(6-2b),2(6-3b),3(6-4b))with methyl propiolate and dimethyl-acetylenedicarboxylate(DMAD)give two types of products,zwitterionic heterocycles[2,4,6-Me3C6H2N(PPh2)SiCl3](HC=CCO2Me)(6-5c)and[ArN(PPh2)SiMenCl3-n](Me02CC=CC02Me)(Ar?2,4,6-Me3C6H2,n?0(6-5a),1(6-6a),2(6-7a);Ar=2,6-iPr2C6H3,n=0(6-5b),1(6-6b),2(6-7b))and(Z)-silylimino-phosphoranylalkene ArN=P(Ph2)C(CO2Me)=C(CO2Me)SiMe3(Ar?2,4,6-Me3 C6H2(6-8a),2,6-iPr2C6H4(6-8b).The reaction of Me3SiN(PPh2)(SiMe3)with DMAD gives only acyclic alkene Me3SiN=P(Ph2)C(CO2Me)=C(CO2Me)SiMe3(6-9)which is similar to 6-8a,b.In these reactions,compounds 6-la-6-4a and 6-lb-6-4b behave as N-geminal P/Si-based Lewis pairs,which undergo a dipolar cycloaddition reaction with the alkyne to form heterocycles 6-5a-7a,6-5b-7b,and[ArN(PPh2)SiMe3](Me02CC=CCO2Me)(Ar=2,4,6-Me3C6H2(6-8a'),2,6-iPrC6H3(6-8b'))where isolation of 6-8a',b' is not successful.The theoretical calculations indicate a concerted cycloaddition reaction mechanism.The stability of these heterocycles decreases as the number of the Me substituent on the penta-coordinated Si atom increases.Therefore,when the SiMe3 is adopted in 6-4a,b,the heterocycles 6-8a',b' thus formed undergo further ring-opening by the Si-N bond cleavage and concomitant N=P bond formation resulting in 6-8a,b.The formation of the acyclic alkene can be considered as a stepwise SN2 reaction at the silicon center.Furthermore,for comparison,the reaction of ArNHPPh2 with DMAD were investigated,C3NP heterocycles Ph2P[C(CO2Me)CH(OMe)C(O)NAr](Ar=2,4,6-Me3C6H2,(6-10);2,6-iPr2C6H3,(6-11))were obtained along with the migration of proton NH?Then Ph2NPPh2 reacts DMAD to afford Ph2N-[(MeO2C)C=C(CO2Me)]2-PPh2(6-12).6-la-6-12 were characterized by NMR spectrum and 6-5a-6-6b,6-7b,6-8b,6-9-6-12 were further by X-ray single crystal diffraction.6.1,1-Carboboration reaction chemistry of bis(alkynl)aluminum compounds using B(C6F5)3.The 1,1-carboboration reactions using bis(alkynl)aluminum compounds and B(C6F5)3 were studied.This is an effective way to aluminacyclopentadienes so far reported.A seris of ?-diketiminato ligand stablized bis(alkynl)aluminum compounds L1AlC=CR)2(L1=Nacnac=CH(Me C=NAr)2,Ar=2,6-iPr2C6H3,R=Ph(7-1);tBu(7-2);SiMe3 7-3)were prepared,of which only compound 7-1 was able to readily reacted with B(C6Fs)3,affording aluminacyclopentadiene L1AlC(Ph)C(B(C6F5)2)C(C6F5)C(Ph)(7-4)via two steps of the 1,1-carboboration reaction.Similar ligand ligated alkynylaluminum L2Al(C=CPh)2(L2?oC6H4(CH=NAr)(NAr),Ar?2,6-iPr2C6H3,(7-5))reacted with B(C6Fs)3 to afford another aluminacyclopentadiene L2AlC(Ph)C(B(C6F5)2)C(C6F5)C(Ph)(7-6).Bis(phenylenthynl)aluminum L3Al(C-=CPh)2(L3=tBuC(NCy)2(7-7))reacted with B(C6F5)3 by one step 1,1-carboboration to produce L3Al(Ph)C=C(C6F5)[B(C6F5)2(C=CPh)](7-8).All of compounds 7-2-7-8 were characterized by NMR spectroscopy,of which 7-4,7-6 and 7-8 were further authenticated by X-ray crystallography.