Sulfonamide-Supported Aluminum Catalysts for the Ring-Opening Polymerization of <i>rac</i>-Lactide

The synthesis, structures, and ring-opening polymerization (ROP) capability of a wide range of sulfonamide-supported aluminum alkyl and alkoxide complexes are reported. The synthesis of the new protio-ligands PhCH2N(CH2CH2NHSO2R)2 (R = Tol (15, H2N2TsNPh) or Me (16, H2N2MsNPh)) is described. These and the previously reported 1,2-C6H10(NHSO2R)2 (R = Tol (11, H2CyN2Ts) or Mes (12, H2CyN2SO2Mes)) and RCH2N(CH2CH2NHSO2Tol)2 (R = MeOCH2 (13, H2N2TsNOMe) or 2-NC5H4 (14, H2N2TsNpy)) reacted with AlEt3 to form Al(CyN2Ts)Et(THF) (17), Al(CyN2SO2Mes)Et(THF) (18), and Al(N2TsNR)Et (R = Ph (19), OMe (20), or py (21)), respectively. Subsequent reaction of these ethyl complexes with R′OH (R′ = iPr or Bn) resulted in protonolysis of the sulfonamide supporting ligands to yield a mixture of products including Al(OR′)3. In contrast, reaction of Al(OR′)Et2 (R′ = iPr, Bn, CH2CH2NH2, or CH2CH2NMe2) with various protio-ligands formed the sulfonamide-supported alkoxides Al(N2TsNpy)(OR′) (R′ = iPr (22) or Bn (23)), Al(N2MsNPh)(OR′) (R′ = iPr (26) or Bn (27)), Al(N2TsNR)(OCH2CH2NH2) (R = Ph (29), OMe (30), or py (31)), Al(CyN2Ts)(OCH2CH2NMe2) (32), and Al(N2TsNPh)(OCH2CH2NMe2) (33). Unexpectedly, reaction of Al(OiPr)Et2 with H2N2TsNOMe led to O-demethylation of the sulfonamide ligand. Reaction of AlMe2Cl with H2N2TsNPh gave [Al(NTs2NPh)Cl]2 (28). X-ray diffraction studies revealed four- or five-coordinate Cs-symmetric structures for 17−21, a five-coordinate C2-symmetric sulfonamide-bridged dimer for 28, and a five-coordinate Cs-symmetric monomer for 30 stabilized by intramolecular hydrogen bonding between the sulfonyl oxygens and the amine protons. Compounds 19, 21, 22−27, and 29−33 are all catalysts for the ROP of rac-lactide, with the alkoxide compounds 22−27 and 32 giving well-defined molecular weights and molecular weight distributions. These compounds were also active in the melt at 130 °C, giving atactic poly(rac-lactide) with moderate to narrow PDIs and extremely good control of Mn and high activity in the case of 23

Sulfonamide-Supported Aluminum Catalysts for the Ring-Opening Polymerization of <i>rac</i>-Lactide

The synthesis, structures, and ring-opening polymerization (ROP) capability of a wide range of sulfonamide-supported aluminum alkyl and alkoxide complexes are reported. The synthesis of the new protio-ligands PhCH2N(CH2CH2NHSO2R)2 (R = Tol (15, H2N2TsNPh) or Me (16, H2N2MsNPh)) is described. These and the previously reported 1,2-C6H10(NHSO2R)2 (R = Tol (11, H2CyN2Ts) or Mes (12, H2CyN2SO2Mes)) and RCH2N(CH2CH2NHSO2Tol)2 (R = MeOCH2 (13, H2N2TsNOMe) or 2-NC5H4 (14, H2N2TsNpy)) reacted with AlEt3 to form Al(CyN2Ts)Et(THF) (17), Al(CyN2SO2Mes)Et(THF) (18), and Al(N2TsNR)Et (R = Ph (19), OMe (20), or py (21)), respectively. Subsequent reaction of these ethyl complexes with R′OH (R′ = iPr or Bn) resulted in protonolysis of the sulfonamide supporting ligands to yield a mixture of products including Al(OR′)3. In contrast, reaction of Al(OR′)Et2 (R′ = iPr, Bn, CH2CH2NH2, or CH2CH2NMe2) with various protio-ligands formed the sulfonamide-supported alkoxides Al(N2TsNpy)(OR′) (R′ = iPr (22) or Bn (23)), Al(N2MsNPh)(OR′) (R′ = iPr (26) or Bn (27)), Al(N2TsNR)(OCH2CH2NH2) (R = Ph (29), OMe (30), or py (31)), Al(CyN2Ts)(OCH2CH2NMe2) (32), and Al(N2TsNPh)(OCH2CH2NMe2) (33). Unexpectedly, reaction of Al(OiPr)Et2 with H2N2TsNOMe led to O-demethylation of the sulfonamide ligand. Reaction of AlMe2Cl with H2N2TsNPh gave [Al(NTs2NPh)Cl]2 (28). X-ray diffraction studies revealed four- or five-coordinate Cs-symmetric structures for 17−21, a five-coordinate C2-symmetric sulfonamide-bridged dimer for 28, and a five-coordinate Cs-symmetric monomer for 30 stabilized by intramolecular hydrogen bonding between the sulfonyl oxygens and the amine protons. Compounds 19, 21, 22−27, and 29−33 are all catalysts for the ROP of rac-lactide, with the alkoxide compounds 22−27 and 32 giving well-defined molecular weights and molecular weight distributions. These compounds were also active in the melt at 130 °C, giving atactic poly(rac-lactide) with moderate to narrow PDIs and extremely good control of Mn and high activity in the case of 23

Sulfonamide-Supported Group 4 Catalysts for the Ring-Opening Polymerization of ε-Caprolactone and <i>rac</i>-Lactide

Reaction of RCH2N(CH2CH2NHSO2Tol)2 (R = 2-NC5H4 (8, H2Lpy) or MeOCH2 (9, H2LOMe)) with Ti(NMe2)4 at room temperature afforded Ti(Lpy)(NMe2)2 (10) or Ti(LOMe)(NMe2)2 (11), respectively, which contain tetradentate bis(sulfonamide)amine ligands. The corresponding reactions with Ti(OiPr)4 or Zr(OiPr)4·HOiPr required more forcing conditions to form the homologous bis(isopropoxide) analogues, M(LR)(OiPr)2 (M = Ti, R = py (12) or OMe (14); M = Zr, R = py (13) or OMe (15)). Reaction of Ti(NMe2)2(OiPr)2 with H2LR formed 12 or 14 under milder conditions. The X-ray structures of 10−15 have been determined revealing Cs symmetric, 6-coordinate complexes except for 13 which is 7-coordinate with one κ2(N,O) bound sulfonamide donor. Compounds 10− 15 are all catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, with the isopropoxide compounds being the fastest and best controlled, especially in the case of zirconium. In addition, Zr(LOMe)(OiPr) 2 (15) was an efficient catalyst for the well-controlled ROP of rac-lactide both in toluene at 100 °C and in the melt at 130 °C, giving atactic poly(rac-lactide). The polymerization rates and control achieved for 13 and 15 are comparable to those of the well-established bis(phenolate)amine-supported Group 4 systems reported recently

Sulfonamide-Supported Group 4 Catalysts for the Ring-Opening Polymerization of ε-Caprolactone and <i>rac</i>-Lactide

Reaction of RCH2N(CH2CH2NHSO2Tol)2 (R = 2-NC5H4 (8, H2Lpy) or MeOCH2 (9, H2LOMe)) with Ti(NMe2)4 at room temperature afforded Ti(Lpy)(NMe2)2 (10) or Ti(LOMe)(NMe2)2 (11), respectively, which contain tetradentate bis(sulfonamide)amine ligands. The corresponding reactions with Ti(OiPr)4 or Zr(OiPr)4·HOiPr required more forcing conditions to form the homologous bis(isopropoxide) analogues, M(LR)(OiPr)2 (M = Ti, R = py (12) or OMe (14); M = Zr, R = py (13) or OMe (15)). Reaction of Ti(NMe2)2(OiPr)2 with H2LR formed 12 or 14 under milder conditions. The X-ray structures of 10−15 have been determined revealing Cs symmetric, 6-coordinate complexes except for 13 which is 7-coordinate with one κ2(N,O) bound sulfonamide donor. Compounds 10− 15 are all catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, with the isopropoxide compounds being the fastest and best controlled, especially in the case of zirconium. In addition, Zr(LOMe)(OiPr) 2 (15) was an efficient catalyst for the well-controlled ROP of rac-lactide both in toluene at 100 °C and in the melt at 130 °C, giving atactic poly(rac-lactide). The polymerization rates and control achieved for 13 and 15 are comparable to those of the well-established bis(phenolate)amine-supported Group 4 systems reported recently

Sulfonamide, Phenolate, and Directing Ligand-Free Indium Initiators for the Ring-Opening Polymerization of <i>rac</i>-Lactide

Reaction of In(CH2SiMe3)3 with H2N2TsNpy or H2N2TsNOMe gave the five-coordinate indium alkyls In(N2TsNpy)(CH2SiMe3) (14) and In(N2TsNOMe)(CH2SiMe3) (15). The corresponding reaction with H2N2TsNPh gave four-coordinate In(N2TsNPh)(CH2SiMe3) (16). Reaction of H2N2TsNpy with In{N(SiMe3)2}3 gave the amide In(N2TsNpy){N(SiMe3)2} (19). Reaction of Na2N2TsNpy with InCl3 in THF followed by LiOiPr gave the “ate” product In(N2TsNpy)(OiPr)Cl{Li(THF)} (21). The chloride complex In(N2TsNpy)Cl(py) (22) was also isolated. Reaction of In(CH2SiMe3)3 with H2O2MeNpy gave the bis(phenolate)amine compound In(O2MeNpy)(CH2SiMe3) (23), and reaction with iPrOH or Me2NCH2CH2OH gave the mixed alkyl-alkoxides In(CH2SiMe3)2(OiPr) (17) and In(CH2SiMe3)2(OCH2CH2NMe2) (18), which are dimeric in the solid state. The X-ray structures of 14, 15, 17−19, and 21 − 23 have been determined. The compounds were evaluated as initiators for the ring-opening polymerization of rac-lactide. With the alkyl and amide initiators, the Mn control was poor because of an unfavorable mismatch between initiation and propagation rates. The molecular weight control with the “ate” complex 21 was better, but the ROP was slow. The best-behaved initiator in terms of living ROP was In(CH2SiMe3)2(OiPr) (17). When used alone, In(CH2SiMe3)3 was a very poor initiator, but in the presence of BnNH2 amine-co-initiated immortal ROP occurred to give atactic amine-terminated PLA in a controlled manner. Use of InCl3 and Et3N in place of the indium alkyl gave a 4-fold increase in activity and a substantial increase in heterotacticity (Pr = 0.85). Initial studies showed that BnNH2 and InCl3 alone could also produce heterotactically enriched, amine-terminated PLA at room temperature, albeit very slowly. (H2N2TsNpy = (2-NC5H4)CH2N(CH2CH2NHTs)2; H2N2TsNOMe = MeOCH2CH2N(CH2CH2NHTs)2; H2N2TsNPh = PhCH2N(CH2CH2NHTs)2; H2O2MeNpy = (2-NC5H4)CH2N(CH2ArOH)2 (Ar = C6H2Me2).

Sulfonamide, Phenolate, and Directing Ligand-Free Indium Initiators for the Ring-Opening Polymerization of <i>rac</i>-Lactide

Reaction of In(CH2SiMe3)3 with H2N2TsNpy or H2N2TsNOMe gave the five-coordinate indium alkyls In(N2TsNpy)(CH2SiMe3) (14) and In(N2TsNOMe)(CH2SiMe3) (15). The corresponding reaction with H2N2TsNPh gave four-coordinate In(N2TsNPh)(CH2SiMe3) (16). Reaction of H2N2TsNpy with In{N(SiMe3)2}3 gave the amide In(N2TsNpy){N(SiMe3)2} (19). Reaction of Na2N2TsNpy with InCl3 in THF followed by LiOiPr gave the “ate” product In(N2TsNpy)(OiPr)Cl{Li(THF)} (21). The chloride complex In(N2TsNpy)Cl(py) (22) was also isolated. Reaction of In(CH2SiMe3)3 with H2O2MeNpy gave the bis(phenolate)amine compound In(O2MeNpy)(CH2SiMe3) (23), and reaction with iPrOH or Me2NCH2CH2OH gave the mixed alkyl-alkoxides In(CH2SiMe3)2(OiPr) (17) and In(CH2SiMe3)2(OCH2CH2NMe2) (18), which are dimeric in the solid state. The X-ray structures of 14, 15, 17−19, and 21 − 23 have been determined. The compounds were evaluated as initiators for the ring-opening polymerization of rac-lactide. With the alkyl and amide initiators, the Mn control was poor because of an unfavorable mismatch between initiation and propagation rates. The molecular weight control with the “ate” complex 21 was better, but the ROP was slow. The best-behaved initiator in terms of living ROP was In(CH2SiMe3)2(OiPr) (17). When used alone, In(CH2SiMe3)3 was a very poor initiator, but in the presence of BnNH2 amine-co-initiated immortal ROP occurred to give atactic amine-terminated PLA in a controlled manner. Use of InCl3 and Et3N in place of the indium alkyl gave a 4-fold increase in activity and a substantial increase in heterotacticity (Pr = 0.85). Initial studies showed that BnNH2 and InCl3 alone could also produce heterotactically enriched, amine-terminated PLA at room temperature, albeit very slowly. (H2N2TsNpy = (2-NC5H4)CH2N(CH2CH2NHTs)2; H2N2TsNOMe = MeOCH2CH2N(CH2CH2NHTs)2; H2N2TsNPh = PhCH2N(CH2CH2NHTs)2; H2O2MeNpy = (2-NC5H4)CH2N(CH2ArOH)2 (Ar = C6H2Me2).

Ligand Variations in New Sulfonamide-Supported Group 4 Ring-Opening Polymerization Catalysts

The synthesis, structures, and ring-opening polymerization (ROP) capability of a wide range of sulfonamide-supported group 4 amide, alkyl, and alkoxide complexes, varying in sulfonamide N-substituent, metal, coordination number, and geometry, are reported. Reaction of Ti(NMe2)4 or Ti(NMe2)2(OiPr)2 with MeOCH2CH2N(CH2CH2NHSO2Me)2 (12, H2N2MsNOMe) or PhCH2N(CH2CH2NHSO2R)2 (R = Tol (10, H2N2TsNPh) or Me (11, H2N2MsNPh)) afforded Ti(N2MsNOMe)(NMe2)2 (18), Ti(N2TsNPh)(NMe2)2 (19), Ti(N2MsNPh)(NMe2)2 (20), Ti(N2MsNOMe)(OiPr)2 (21), Ti(N2TsNPh)(OiPr)2 (22), Ti(N2MsNPh)(OiPr)2 (23), and Ti(N2TsNPh)(OiPr)(NMe2) (24). Reaction of N(CH2CH2NHSO2R)3 (R = Tol (13, H3N3TsN), Me (14, H3N3MsN), or ArF (15, H3N3ArFN, ArF = 3,5-C6H3(CF3)2)) with Zr(CH2SiMe3)4 formed Zr(N3RN)(CH2SiMe3) (R = Ts (30), Ms (31), or ArF (32)). Reaction of 15 with Zr(NMe2)4 gave Zr(N3ArFN)(NMe2) (33). Complexes 19, 21, 24, 30, 32, and 33 were crystallographically characterized. Monomeric six- or five-coordinate structures were found for the titanium complexes 19, 21, and 24, whereas the zirconium alkyls 30 and 32 were dimeric in the solid state with terminal and bridging κ2(N,O)-bound sulfonamides. Complexes 18−24 and 30−33, the previously reported Ti(CyN2R)(OiPr)2 (25 or 26; CyN2R = 1,2-C6H10(NSO2Tol)2 or 1,2-C6H10(NSO2Mes)2), and in situ generated isopropoxide initiators derived from 30−32 were investigated for the ROP of ε-caprolactone (ε-CL). The four-coordinate 25 was the most active, forming poly(ε-CL) with a relatively narrow PDI and well-controlled Mn. Compounds 22, 23, 25, and 26 and isopropoxides generated in situ from 30−32 were all active for the ROP of rac-lactide. Of these, the initiators based on Zr(N3RN)(CH2SiMe3) (30−32) with iPrOH co-initiator gave good activities and excellent PDIs (1.08−1.11) and agreement between measured and predicted Mn

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

This paper reports a general method for the synthesis of new terminal titanium diphenyl hydrazido(2−) complexes containing dianionic N3- and N4-donor ligands, along with new hydrazido synthons. Reaction of Ti(NtBu)Cl2(py)3 or Ti(NtBu)Cl2(py′)3 (py′ = 4-NC5H4tBu) with Ph2NNH2 gave excellent yields of the corresponding monomeric hydrazides Ti(NNPh2)Cl2(L)3 (L = py (7) or py′), which have been structurally characterized. Application of a dynamic vacuum to 7 formed [Ti(NNPh2)Cl2(py)2]2 (4). Both 4 and 7 are entry points to new titanium hydradizo complexes on reaction with metalated reagents. In this way, four new five-coordinate diamide-amine complexes Ti(NNPh2)(“N2N”)(py) were made (“N2N” = MeN(CH2CH2NSiMe3)2, Me3SiN(CH2CH2NSiMe3)2, MeN(CH2CH2CH2NSiMe3)2, (2-NC5H4)C(Me)(CH2NSiMe3)2) and structurally characterized. Five- and six-coordinate terminal titanium hydrazides containing dianionic N4- or O2N2-donor ligands were also synthesized from 4 by an analogous method. The identity of the “N2N” ligand affects the TiNα and Nα−Nβ distances of the TiN−NPh2 functional group. A detailed DFT analysis of the bonding in these and a range of model complexes is presented using molecular orbital and natural bond orbital methods. The competition between N(amide) and N(hydrazide) Ti(3dπ)−N(2pπ) interactions has an indirect and significant effect on the Nα−Nβ bond

Synthesis, Structures and Reactivity of Group 4 Hydrazido Complexes Supported by Calix[4]arene Ligands

Reaction of TiCl2(Me2Calix) with 2 equiv of LiNHNRR′ afforded the corresponding terminal hydrazido(2-) complexes Ti(NNRR′)(Me2Calix) (R = Ph, R′ = Ph (1) or Me; R = R′ = Me (3)) which were all structurally characterized. The X-ray structure of Ph2NNH2 is reported for comparison. Compound 1 was also prepared from Na2[Me2Calix] and Ti(NNPh2)Cl2(py)3. Reaction of ZrCl2(Me2Calix) with 2 equiv of LiNHNR2 afforded only the bis(hydrazido(1-)) complexes Zr(NHNR2)2(Me2Calix) (R = Ph or Me). Treatment of Ti(NNMe2)(Me2Calix) (3) with MeI gave the zwitterionic hydrazidium species Ti(NNMe3)(MeCalix) (6) via a net isomerization reaction which was found to be catalytic in MeI. The corresponding reaction of 3 with CD3I gave Ti(NNMe2CD3)(MeCalix) (6-d3) with concomitant elimination of MeI. Reaction of 3 with 1 equiv of MeOTf gave [Ti(NNMe3)(Me2Calix)][OTf] (7-OTf) which in turn reacted with nBu4NI to form 6 and MeI. Addition of PhCHO to 3 gave the μ-oxo dimer [Ti(μ-O)(Me2Calix)]2 and benzaldehyde-dimethylhydrazone. Reaction of either 3 or 6 with tBuNCO gave the zwitterionic species Ti{tBuNC(NNMe3)O}(MeCalix) (10) which has been crystallographically characterized. Compound 10 is the formal product of insertion of an isocyanate into the TiNα bond of a titanium hydrazide or hydrazidium species (Me2Calix or MeCalix = dianion or trianion of the di- or monomethyl ether of p-tert-butyl calix[4]arene, respectively)

New Sandwich and Half-Sandwich Titanium Hydrazido Compounds

New mono- and bis-cyclopentadienyl terminal titanium hydrazido(2−) compounds were prepared by tert-butyl imide/N,N-disubstituted hydrazine exchange reactions. Reaction of Cp*Ti(NtBu)Cl(py) (1) with Ph2NNH2 gave the terminal hydrazide Cp*Ti(NNPh2)Cl(py) (4), whereas the corresponding reaction of CpTi(NtBu)Cl(py) gave the dimer Cp2Ti2(μ-η1:η1-NNPh2)(μ-η2:η1-NNPh2)Cl2. Reaction of 1 with Me2NNH2 (1 equiv) also gave a dimer, Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8), while the reaction with 2 equiv of Me2NNH2 gave Cp*Ti(η2-NHNMe2)2Cl (7) containing two η2-bound hydrazide(1−) ligands. Formation of 7 and 8 proceeds via a common intermediate, Cp*Ti(NHtBu)(η2-NHNMe2)Cl, observed by NMR spectroscopy. Reaction of 4 with LiNHNPh2 gave the mixed hydrazide(2−)/hydrazide(1−) derivative Cp*Ti(NNPh2)(NHNPh2)(py) (10). The corresponding reaction of 1 formed Cp*Ti(NtBu)(NHNPh2)(py), which rearranged to Cp*Ti(NHtBu)(NNPh2)(py). The titanocene derivative Cp2Ti(NNPh2)(py) (14) was prepared by reaction of Cp2Ti(NtBu)(py) (13) with Ph2NNH2, whereas the corresponding reaction with Me2NNH2 gave mixtures including CpTi(NHtBu)(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)TiCp(η1-Cp). The electronic structure of 14 was investigated by DFT and compared to that of the imido complex 13. Whereas the HOMO of the formally 20 valence electron compound 13 is a ligand-centered orbital based both on the Cp rings and on the imido N, in 14 this is the HOMO−1 and one of the TiNα π-bonding MOs is the HOMO, destabilized by an Nα−Nβ antibonding interaction