Density functional theory and CCSD(T) evaluation of ionization potentials, redox potentials, and bond energies related to zirconocene polymerization catalysts.

Quantum-mechanical-based computational design of molecular catalysts requires accurate and fast electronic structure calculations to determine and predict properties of transition-metal complexes. For Zr-based molecular complexes related to polyethylene catalysis, previous evaluation of density functional theory (DFT) and wavefunction methods only examined oxides and halides or select reaction barrier heights. In this work, we evaluate the performance of DFT against experimental redox potentials and bond dissociation enthalpies (BDEs) for zirconocene complexes directly relevant to ethylene polymerization catalysis. We also examined the ability of DFT to compute the fourth atomic ionization potential of zirconium and the effect the basis set selection has on the ionization potential computed with CCSD(T). Generally, the atomic ionization potential and redox potentials are very well reproduced by DFT, but we discovered relatively large deviations of DFT-calculated BDEs compared to experiment. However, evaluation of BDEs with CCSD(T) suggests that experimental values should be revisited, and our CCSD(T) values should be taken as most accurate.

A Manganese Pre-Catalyst: Mild Reduction of Amides, Ketones, Aldehydes, and Esters.

A new (N-phosphinoamidinate)manganese complex is shown to be a useful pre-catalyst for the hydrosilative reduction of carbonyl compounds, and in most cases at room temperature. The Mn-catalyzed reduction of tertiary amides to tertiary amines, with a useful scope, is demonstrated for the first time by use of this catalyst, and is competitive with the most effective transition-metal catalysts known for such transformations. Ketones, aldehydes, and esters were also successfully reduced under mild conditions by using this new Mn catalyst.

Dehydrogenative B-H/C(sp3 )-H Benzylic Borylation within the Coordination Sphere of Platinum(II).

The first examples of stoichiometric dehydrogenative B-H/C(sp3 )-H benzylic borylation reactions, which are of relevance to catalytic methylarene (di)borylation, are reported. These unusual transformations involving a (κ2 -P,N)Pt(η3 -benzyl) complex, and either pinacolborane or catecholborane, proceed cleanly at room temperature. Density functional calculations suggest that borylation occurs via successive σ-bond metathesis steps, whereby a PtII -H intermediate engages in C(sp3 )-H bond activation-induced dehydrogenation.

Synthesis and Reactivity of a Neutral, Three-Coordinate Platinum(II) Complex Featuring Terminal Amido Ligation.

A crystallographically characterized three-coordinate, formally 14 electron Pt(II) complex 1 featuring terminal amido ligation is reported. Computational analysis revealed relatively weak π donation from the amide lone pair to platinum and supports a 14-electron assignment for 1. Stoichiometric reactivity studies confirmed the viability of net O-H and C-H addition across, as well as isonitrile insertion into, the terminal platinum-amido linkage of 1.

(N-phosphinoamidinate)cobalt-catalyzed hydroboration: alkene isomerization affords terminal selectivity.

Herein we establish the utility of a three-coordinate (N-phosphinoamidinate)cobalt(amido) pre-catalyst that is capable of effecting challenging alkene isomerization/hydroboration processes at room temperature, leading to the selective terminal addition of the boron group.

Quantum-mechanical transition-state model combined with machine learning provides catalyst design features for selective Cr olefin oligomerization.

The use of data science tools to provide the emergence of non-trivial chemical features for catalyst design is an important goal in catalysis science. Additionally, there is currently no general strategy for computational homogeneous, molecular catalyst design. Here, we report the unique combination of an experimentally verified DFT-transition-state model with a random forest machine learning model in a campaign to design new molecular Cr phosphine imine (Cr(P,N)) catalysts for selective ethylene oligomerization, specifically to increase 1-octene selectivity. This involved the calculation of 1-hexene : 1-octene transition-state selectivity for 105 (P,N) ligands and the harvesting of 14 descriptors, which were then used to build a random forest regression model. This model showed the emergence of several key design features, such as Cr-N distance, Cr-α distance, and Cr distance out of pocket, which were then used to rapidly design a new generation of Cr(P,N) catalyst ligands that are predicted to give >95% selectivity for 1-octene.

Synthetic investigations of low-coordinate (N-phosphino-amidinate) nickel chemistry: agostic alkyl complexes and benzene insertion into Ni-H.

Treatment of (PN)NiX (X = NHdipp or OtBu; PN = N-phosphinoamidinate ligand) with Me2PhSiH in benzene solvent afforded the crystallographically characterized, antifacial-coordinated, dinuclear species 1, the formation of which corresponds to the hitherto unknown net Ni-H addition of two equivalents of the putative (PN)NiH intermediate across C[double bond, length as m-dash]C units within a single benzene molecule. Computational analysis supports the view of 1 as being comprised of two cationic (PN)NiII fragments ligated by a substituted butadiene dianion µ2-η3:η3-C6H82- bridging group. Also described is the formation and characterization of three-coordinate (PN)Ni(alkyl) complexes stabilized by ß-agostic (alkyl = Et, 2; n-Bu, 3; n-hexyl, 4) or γ-agostic (alkyl = neopentyl, 5) interactions, and our efforts to employ 2 and 3 as synthons for the generation of (PN)NiHvia ß-hydride elimination. Notably, compound 5 represents both the first crystallographically characterized three-coordinate Ni-alkyl complex featuring a heterobidentate ligation, and the first neutral γ-agostic NiII-alkyl complex.

A comparative analysis of hydrosilative amide reduction catalyzed by first-row transition metal (Mn, Fe, Co, and Ni) N-phosphinoamidinate complexes.

A comparative study of the performance of (PN)M(N(SiMe3)2) (M = Mn, Fe, Co, and Ni) pre-catalysts supported by N-phosphinoamidinate ligation, as well as M(N(SiMe3)2)n (M = Li, Na, K, Mn, Fe, and Co) pre-catalysts, in the hydrosilative reduction of selected tertiary amide test substrates using PhSiH3 is reported. Encouraged by the performance observed herein for (PN)Ni(N(SiMe3)2) in the reduction of both N,N-dibenzylbenzamide and N,N-diisopropylbenzamide, further competitive testing involving the known complex (PN)Ni(NHdipp) (dipp = 2,6-diisopropylphenyl), as well as the new and crystallographically characterized mononuclear complexes (PN)Ni(OR) (R = 2,6-dimethylphenyl or tBu), revealed (PN)Ni(OtBu) to be particularly effective in such reduction chemistry, including transformations involving the secondary amides N-benzylbenzamide and caprolactam.

First row wheels, [((t)Bu(3)SiS)MX](12)(M = Co, X = Cl; M = Ni, X = Br), are common amongst both simpler and more complex aggregates.

[((t)Bu(3)SiS)MX[(12) are wheels for first row transition metals (M = Co, X = Cl; M = Ni, X = Br), but for nickel, simpler [e.g. [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2)[ and more complicated [e.g. [(mu-SSi(t)Bu(3))Ni](5)(mu(5)-S)] structures are by-products.

Aggregation of [(tBu3SiS)MX]: structures of {[Br2Fe(mu-SSitBu3)2)FeBr(THF)]Na(THF)4}infinity, cis-[(THF)FeI]2(mu-SSitBu3)2, [(tBu3SiS)Fe]2(mu-SSitBu3)2, and comparative structure and magnetism studies of [(tBu3SiS)MX]n (M = Fe, Co, X = Cl, n = 12; M = Fe, Ni, X = Br, n = 12; M = Fe, X = I, n = 14).

A convenient synthesis of (t)Bu(3)SiSH and (t)Bu(3)SiSNa(THF)(x)() led to the exploration of "(t)Bu(3)SiSMX" aggregation. The dimer, [((t)Bu(3)SiS)Fe](2)(mu-SSi(t)Bu(3))(2) (1(2)), was formed from [{(Me(3)Si)(2)N}Fe](2)(mu-N(SiMe(3))(2))(2) and the thiol, and its dissolution in THF generated ((t)Bu(3)SiS)(2)Fe(THF)(2) (1-(THF)(2)). Metathetical procedures with the thiolate yielded aggregate precursors [X(2)Fe](mu-SSi(t)Bu(3))(2)[FeX(THF)]Na(THF)(4) (3-X, X = Cl, Br) and cis-[(THF)IFe](2)(mu-SSi(t)Bu(3))(2) (4). Thermal desolvations of 3-Cl, 3-Br and 4 afforded molecular wheels [Fe(mu-X)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-FeX, X = Cl, Br) and the ellipse [Fe(mu-I)(mu-SSi(t)Bu(3))](14)(C(6)H(6))(n) (6-FeI). Related metathesis and desolvation sequences led to wheels [Co(mu-Cl)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-CoCl) and [Ni(mu-Br)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-NiBr). The nickel wheel disproportionated to give, in part, [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2) (7), which was also synthesized via salt metathesis. X-ray structural studies of 1(2) revealed a roughly planar Fe(2)S(4) core, while 1-(THF)(2), 3-Br, and 4 possessed simple distorted tetrahedral and edge-shared tetrahedral structures. X-ray structural studies revealed 5-MX (MX = FeCl, FeBr, CoCl, NiBr) to be wheels based on edge-shared tetrahedra, but while the pseudo-D(6)(d) wheels of 5-FeCl, 5-CoCl, and 5-FeBr pack in a body-centered arrangement, those of pseudo-C(6)(v)() 5-NiBr exhibit hexagonal packing and two distinct trans-annular d(Br...Br). Variable-temperature magnetic susceptibility measurements were conducted on 5-FeCl, 5-CoCl, 5-FeBr, and 6-FeI, and the latter three are best construed as weakly antiferromagnetic, while 5-FeCl exhibited modest ferromagnetic coupling. Features suggesting molecular magnetism are most likely affiliated with phase changes at low temperatures.

The butterfly dimer [(tBu3SiO)Cr]2(mu-OSitBu3)2 and its oxidative cleavage to (tBu3SiO)2Cr(=N-N=CPh2)2 and (tBu3SiO)2Cr=N(2,6-Ph2-C6H3).

Treatment of CrCl2(THF)2 with NaOSitBu3 afforded the butterfly dimer [(tBu3SiO)Cr]2(mu-OSitBu3)2 (1(2)), whose d(CrCr) of 2.658(31) A and magnetism were indicative of strong antiferromagnetic coupling. A Boltzmann distribution of low-energy 1A1, 3B1, 5A1, 7B1, and 9A1 states obtained from calculations on [(HO)2Cr]2(muOH)2 (1'(2)) were used to provide a reasonable fit of the mu(eff) vs T data. Cleavage of 1(2) with various L (L = 4-picoline, p-tolunitrile, tBuCN, tBuNC, Ph2CO, and PMe3) generated (tBu3SiO)2CrL2 (1-L2). The dimer was oxidatively severed by Ph2CN2 to give (tBu3SiO)2Cr(N2CPh2)2 (2) and by RN3 at 23 degrees C to afford (silox)2Cr=NR (3-R) for bulky R (adamantyl (Ad), 2,6-iPr2-C6H3, 2,4,6-Me3-C6H2 = Mes, 2,6-Ph2-C6H3) and (tBu3SiO)2Cr(=NR)2 (4-R) for smaller substituents (R = 1-Naph, 2-Anth). X-ray structural studies were conducted on 1(2), square planar 1-(OCPh2)2, pseudo-Td 2 and pseudo-trigonal 3-(2,6-Ph2-C6H3), whose S = 1 ground state was discussed on the basis of calculations of (H3SiO)2Cr=NPh (3' '-Ph).

Low-coordinate chromium siloxides: the "box" [Cr(mu-Cl)(mu-OSitBu3)]4, distorted trigonal [(tBu3SiO)3Cr][Na(benzene)] and [(tBu3SiO)3Cr][Na(dibenzo-18-c-6)], and trigonal (tBu3SiO)3Cr.

Treatment of CrCl(2)(THF)(2) with NaOSi(t)Bu(3) afforded the tetrameric "box" [Cr(mu-Cl)(mu-OSi(t)Bu(3))](4) (1, X-ray). THF cleaved 1 to provide trans-(silox)ClCr(THF)(2) (2), whereas degradation of 1 with 4-picoline caused disproportionation and the generation of trans-Cl(2)Cr(4-pic)(2) and trans-(silox)(2)Cr(4-pic)(x) (n = 2, 3; 3, 3-4-pic). Chromous centers in 1 were antiferromagnetically coupled, and density functional calculations on the high-spin (multiplicity = 17) model [Cr(mu-Cl)(mu-OH)](4) (1') revealed that its singly occupied 3d orbitals spanned an energy range of approximately 2 eV. The addition of 8 equiv of Na(silox) to 1 yielded [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na.C(6)H(6) (4, Y shaped, angle OCrO(Na) = 91.28(7) degrees), and treatment of 4 with dibenzo-18-crown-6 produced [(silox)(3)Cr][Na(dibenzo-18-crown-6)] (5, angle OCrO = approximately 120 degrees, (120 + alpha) degrees, (120 - alpha) degrees). Calculations of [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na (4') and Cr(silox)(3)(-) (5') provided reasonable matches with the experimental geometries (X-ray). The trigonal chromic derivative (silox)(3)Cr (6) was synthesized from CrCl(3)(THF)(3) for structural and calculational comparisons to the chromous derivatives.