Synthesis of Titanium Borylimido Compounds Supported by Diamide-Amine Ligands and Their Reactions with Alkynes

We report a combined synthetic, mechanistic, and computational (DFT) study of the synthesis of new diamide-amine-supported titanium borylimides and their reactions with TolCCH and Ar^FCCH (Tol = 4-C₆H₄Me, Ar^F = C₆F₅). Reaction of Ti­{NB­(NAr′CH)₂}­Cl₂(py)₃ (Ar′ = 2,6-C₆H₃ⁱPr₂) with Li₂N₂^RN^Me (N₂^RN^Me = MeN­(CH₂CH₂NR)₂) or Li₂N₂N^py (N₂N^py = (2-C₅H₄N)­CMe­(CH₂NSiMe₃)₂) afforded the borylimides Ti­(N₂^RN^Me)­{NB­(NAr′CH)₂}­(py) (R = SiMe₃ (<b>9</b>), Ar^F (<b>10</b>), or ⁱPr (<b>11</b>)) and Ti­(N₂N^py)­{NB­(NAr′CH)₂}­(py) (<b>21</b>). Compounds <b>9</b> and <b>10</b> reacted with ArCCH (Ar = Tol or Ar^F) via [2 + 2] cycloaddition to form the azatitanacyclobutenes Ti­(N₂^RN^Me)­{N­{B­(NAr′CH)₂}­C­(H)­C­(Ar)}. In the case of R = Ar^F these underwent subsequent intramolecular C–F bond cleavage/C–C coupling processes. Reaction of <b>11</b> and <b>21</b> with TolCCH also formed azatitanacyclobutenes, whereas Ar^FCCH formed borylamide-acetylides via a C–H bond activation process which is endergonic in the case of TolCCH. On heating, these kinetic products rearranged via alkyne elimination to form the corresponding azatitanacyclobutenes as the thermodynamic outcomes

Synthesis, DFT Studies, and Reactions of Scandium and Yttrium Dialkyl Cations Containing Neutral <i>fac</i>-N₃ and <i>fac</i>-S₃ Donor Ligands

Reaction of Sc(CH2SiMe3)3(THF)2 with 1,4,7-trithiacyclononane gave Sc([9]aneS3)(CH2SiMe3)3, the first organometallic group 3 complex of [9]aneS3 ([9]aneS3 = 1,4,7-trithiacyclononane). The corresponding reaction for yttrium gave equilibrium mixtures of Y([9]aneS3)(CH2SiMe3)3 and starting materials. Density functional theory (DFT) was used to compare the energies of formation and metal−ligand interaction energies for M([9]aneS3)R3 with those for the previously reported fac-N3 donor complexes M(fac-N3)R3 (R = Me or CH2SiMe3; fac-N3 = 1,4,7-trimethyltriazacyclononane (Me3[9]aneN3) or HC(Me2pz)3). Reaction of M(CH2SiMe3)3(THF)2 with [NHMe2Ph][BArF4] (ArF = C6F5) in the presence of a face-capping ligand L (L = HC(Me2pz)3, Me3[9]aneN3, or [9]aneS3) gave the cationic complexes [M(L)(CH2SiMe3)2(THF)]+, which has been structurally characterized for M = Sc and L = [9]aneS3. The corresponding base-free cations [M(L)(CH2SiMe3)2]+ were studied by 29Si NMR spectroscopy and/or DFT and found to possess β-Si−C agostic alkyl groups in most instances. The isolated cations [Sc(fac-N3)(CH2SiMe3)2(THF)]+ underwent THF substitution reactions with OPPh3 or pyridine, Sc−alkyl migratory insertion with carbodiimides, and C−H bond metathesis with PhCCH. The olefin polymerization capabilities of a series of complexes M(L)R3 have been determined. The scandium complexes were found to be very productive for ethylene polymerization for L = HC(Me2pz)3, Me3[9]aneN3, or [9]aneS3 and R = CH2SiMe3 when activated with 1 equiv of [CPh3][BArF4]. When activated with 2 equiv of [CPh3][BArF4], the compounds were also very active for the polymerization of 1-hexene

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

Probing the Limits of Alkaline Earth–Transition Metal Bonding: An Experimental and Computational Study

Reduction of Fp₂ (Fp = CpFe­(CO)₂) or [Co­(CO)₃(PCy₃)]₂ (<b>15</b>) with Mg-mercury amalgam gave [Mg­{TM­(L)}₂(THF)]₂ (TM­(L) = Fp or Co­(CO)₃(PCy₃) (<b>19</b>)) in which the TM is bonded to two Mg atoms. Reduction of <b>15</b> with Ca-, Sr-, Ba-, Yb-, Eu- and Sm-mercury amalgam gave a series of compounds “M­{Co­(CO)₃(PCy₃)}₂(THF)_<i>n</i>” (M = Ae or Ln) in which the M–Co bonding varies with the charge-to-size ratio of M. For M = Ca or Yb (<b>24</b>), each metal forms one M–Co bond and one M­(μ-OC)­Co η¹-isocarbonyl linkage. With M = Sr (<b>21</b>) or Eu (<b>25</b>), a switch from M–Co bonding to side-on (η²) CO ligand coordination is found. Sm^II{Co­(CO)₃(PCy₃)}₂(THF)₃ disproportionates in pentane to form Sm^III{Co­(CO)₃(PCy₃)}₃(THF)₃ containing two Sm^III–Co bonds, in contrast with <b>25</b>, showing the importance of the Ln charge on Ln–TM bonding. Diffusion NMR spectroscopy found that in solution, <b>21</b> and <b>24</b> are dimeric compounds [M­{Co­(CO)₃(PCy₃)}₂(THF)₃]₂ that, according to DFT calculations, contain either one (Ae = Ca) or two (Ae = Sr) Ae–Co bonds per Co atom. DFT calculations in combination with Ziegler Rauk energy decomposition and atoms in molecules analysis were used to assess the nature and energy of Ae–Co bonding in a series of model compounds. The Ae–Co interaction energies decrease from Be to Sr, and toward the bottom of the group, side-on (η²) CO ligand coordination competes with Ae–Co bonding. The PCy₃ ligand plays a pivotal role by increasing solubility in nondonor solvents and the Ae–Co interaction energy

Tantalizing Chemistry of the Half-Sandwich Silylhydride Complexes of Niobium: Identification of Likely Intermediates on the Way to Agostic Complexes

Reactions of the compound [NbCp(ArN)(PMe3)2] with chlorosilanes HSiRR‘Cl give a series of silyl complexes [NbCp(ArN)(PMe3)(H)(SiRR‘Cl)] and [NbCp(ArN)(PMe3)(Cl)(SiRR‘H)] which are likely intermediates to the agostic complexes [NbCp(ArN(RR‘2Si−H···))(PMe3)(Cl)]

Heterobimetallic Complexes Containing Ca–Fe or Yb–Fe Bonds: Synthesis and Molecular and Electronic Structures of [M{CpFe(CO)₂}₂(THF)₃]₂ (M = Ca or Yb)

Reaction of calcium or ytterbium amalgam with [CpFe(CO)2]2 (Fp2) gave the isostructural heavy alkaline earth or divalent rare earth compounds [MFp2(THF)3]2 (M = Ca or Yb) containing two direct Ca–Fe (3.0185(6) Å) or Yb–Fe (2.9892(4) Å) bonds. Density functional theory supports experiment in finding shorter Yb–Fe than Ca–Fe distances, and Ziegler–Rauk, molecular orbital, and atoms-in-molecules analyses find the M–Fe bonding to be predominantly electrostatic in nature. The Yb–Fe interaction energy and bond critical point electron density are slightly larger than for Ca–Fe, in agreement with the shorter M–Fe bond in the former. The corresponding reaction for magnesium gave MgFp2(THF)4 with two O-bound Fp moieties and no Mg–Fe bond

Reactions of Cyclopentadienyl-Amidinate Titanium Imido Compounds with CS₂, COS, Isocyanates, and Other Unsaturated Organic Compounds

New single-, double-, and cross-coupling and imido group transfer reactions of cyclopentadienyl-amidinate titanium imido complexes are described. Reaction of Ti(η-C5R4Me)(NtBu)Cl(py) (R = Me or H) with the lithiated benzamidinate Li[PhC(NSiMe3)2] or acetamidinate Li[MeC(NiPr)2] afforded the tert-butyl imido complexes Ti(η-C5R4Me)(NtBu){PhC(NSiMe3)2} (R = Me (5) or H (7)) and Ti(η-C5R4Me)(NtBu){MeC(NiPr2)2} (R = Me (6) or H (8)), respectively. Reaction of 6 with ArNH2 or TolNH2 (Ar = 2,6-C6H3Me2, Tol = 4-C6H4Me) afforded the corresponding aryl imido complexes Ti(η-C5Me5)(NR){MeC(NiPr2)2} (R = Ar (9) or Tol (10)). Complexes 5, 7, and 8 underwent cycloaddition/extrusion reactions with CS2 and COS to form μ-sulfido dimers and tBuNCS and tBuNCO, respectively. Compound 6 reacted with COS to form tBuNCO and [Ti(η-C5Me5)(μ-S){MeC(NiPr)2}]2, but with CS2 additional insertion into an amidinate ligand Ti−NiPr bond occurred to form [Ti(η-C5Me5)(μ-S){N(iPr)C(Me)N(iPr)C(S)S}]2. For the aryl imido compounds 9 and 10 the intermediate cycloaddition products Ti(η-C5Me5){N(R)C(E)S}{MeC(NiPr)2} (E = S or O) were observed. No further insertion of CS2 or COS into the Ti−NR bonds occurred. All tert-butyl imido compounds reacted slowly with tBuNCO or ArNCO to form μ-oxo-bridged dimers and tBuNCNtBu or tBuNCNAr, respectively. Reaction of 9 with tBuNCO gave the N,O-bound ureate Ti(η-C5Me5){N(Ar)C(NtBu)O}{MeC(NiPr)2}, which extruded tBuNCNAr to form [Ti(η-C5Me5)(μ-O){MeC(NiPr)2}]2. Reaction of 9 or 10 with aryl isocyanates gave the N,O-bound ureates Ti(η-C5Me5){N(R1)C(NR2)O}{MeC(NiPr)2} (R1 = Ar, R2 = Ar or Tol; R1 = Tol, R2 = Ar or Tol (25)), which did not undergo extrusion. Reaction of 25 with TolNCO gave the net cycloaddition−insertion product Ti(η-C5Me5){OC(NTol)NTolC(NTol)O}{MeC(NiPr)2}. Several heterocumulene cross-coupling cycloaddition−insertion reactions were studied:  for example, the sequential reaction of 10 with TolNCO and CO2 gave Ti(η-C5Me5){OC(O)NTolC(NTol)O}{MeC(NiPr)2}. Aryl imides 9 and 10 reacted with TolNCNTol to form the guanidinate complexes Ti(η-C5Me5){N(Tol)C(NTol)N(R)}{MeC(NiPr)2} (R = Ar or Tol). Reaction of 5 and 6 with PhNO gave tBuNNPh and μ-oxo-bridged dimers; the aryl imides 9 and 10 reacted similarly. Ketone and aldehyde CO/TiNR bond metathesis reactions occurred for certain tert-butyl and aryl imido compounds with MeCOMe, PhCOPh, PhCOH, and PhCOMe, and in some instances intermediates were observed. Slow imide/imine metathesis occurred between Ti(η-C5Me5)(N-4-C6H4NMe2){PhC(NiPr2)2} and PhCH(NTol). Compound 6 rapidly converted PhCONH2 and Me(CH2)4CONH2 to the corresponding nitriles, but the analogous reaction with tBuCONH2 was slower. Several other titanium imido compounds and Ti(NMe2)2Cl2 were also evaluated for the PhCONH2 dehydration reaction

Tantalizing Chemistry of the Half-Sandwich Silylhydride Complexes of Niobium: Identification of Likely Intermediates on the Way to Agostic Complexes

Reactions of the compound [NbCp(ArN)(PMe3)2] with chlorosilanes HSiRR‘Cl give a series of silyl complexes [NbCp(ArN)(PMe3)(H)(SiRR‘Cl)] and [NbCp(ArN)(PMe3)(Cl)(SiRR‘H)] which are likely intermediates to the agostic complexes [NbCp(ArN(RR‘2Si−H···))(PMe3)(Cl)]

Heterobimetallic Complexes Containing Ca–Fe or Yb–Fe Bonds: Synthesis and Molecular and Electronic Structures of [M{CpFe(CO)₂}₂(THF)₃]₂ (M = Ca or Yb)

Reaction of calcium or ytterbium amalgam with [CpFe(CO)2]2 (Fp2) gave the isostructural heavy alkaline earth or divalent rare earth compounds [MFp2(THF)3]2 (M = Ca or Yb) containing two direct Ca–Fe (3.0185(6) Å) or Yb–Fe (2.9892(4) Å) bonds. Density functional theory supports experiment in finding shorter Yb–Fe than Ca–Fe distances, and Ziegler–Rauk, molecular orbital, and atoms-in-molecules analyses find the M–Fe bonding to be predominantly electrostatic in nature. The Yb–Fe interaction energy and bond critical point electron density are slightly larger than for Ca–Fe, in agreement with the shorter M–Fe bond in the former. The corresponding reaction for magnesium gave MgFp2(THF)4 with two O-bound Fp moieties and no Mg–Fe bond