Group 4 metalloporphyrin alkoxido, amido, hydrazido, and imido complexes: synthesis and reactivity

Previous examinations of group 4 coordination chemistry have predominately involved cyclopentadienyl, alkoxido, and amido complexes. The systematic exploration of the chemistry of group 4 metalloporphyrin complexes has recently been made possible by facile routes to useful porphyrin starting materials. Of interest are complexes containing hard pi-donor ligands. From these, bonding characteristics and steric constraints of the porphyrin periphery specific to the ligand can be studied;The implementation of the group 4 metal halide complexes, (TTP)MCl 2, in metathesis reactions has provided routes to amido, alkoxido, hydrazido, and imido derivatives. These complexes have subsequently demonstrated unique reactivity properties. It has been found that the formation of zirconium and hafnium imido metalloporphyrin complexes is dependent on the steric bulk of the phenyl substituent of the lithiated amide. Bis(amido) complexes are isolable when the ortho positions of phenyl amide are unsubstituted. The presence of the sterically demanding methyl, tert-butyl, or isopropyl groups at the ortho position of the phenyl amide effects an alpha-elimination of a primary aryl amine from the unstable secondary bis(amido) precursor to produce the imido derivative. These imido compounds were key starting materials for the production and investigation of a number of complexes containing M-O bonds. The zirconium and hafnium imido complexes, (TTP)M= NAriPr , couple two pinacolone molecules with concomitant loss of the amine H2 NAriPr . The hydrazido, (TTP)Ti=NNR2 (R = Me, Ph), and imido, (TTP)Ti=NiPr, derivatives of titanium undergo novel nitrene group metathesis reactions with p-chlorobenzaldehyde and with nitrosobenzene, respectively;Additional examples of atom and group transfer involving titanium(II) metalloporphyrins have been demonstrated. Utilization of a variety of donor molecules has facilitated the estimation of the double bond strength for complexes of the type (TTP)Ti=G (G = O, S, Se, NR). This dissertation focuses on the synthesis and reactivity of group 4 metalloporphyrin complexes containing hard pi-donor ligands and on the properties of titanium(II) metalloporphyrin species

Synthesis and Reactivity of Hydrazido(2-) and Imido Derivatives of Titanium(IV) Tetratolylporphyrin

Titanium porphyrin hydrazido complexes (TTP)TiNNR2 (TTP = meso-tetra-p-tolylporphyrinato dianion; R = Me (1), Ph (2)) were synthesized by treatment of (TTP)TiCl2with 1,1-disubstituted hydrazines H2NNR2 (R = Me, Ph) in the presence of piperidine. The nucleophilic character of the hydrazido moiety was demonstrated in the reactions of complexes 1 and 2 with p-chlorobenzaldehyde, which yielded the titanium oxo complex (TTP)TiO and the respective hydrazones. Protonation of complexes 1 and 2 with phenol or water produced the 1,1-disubstituted hydrazine along with (TTP)Ti(OPh)2 or (TTP)TiO, respectively. Similar reactivity of p-chlorobenzaldehyde and phenol with (TTP)TiNiPr, 3, was observed. The reaction of complex 3 with nitrosobenzene cleanly formed the azo compound iPrNNPh and the terminal oxo product (TTP)TiO

Alkoxido, Amido, and Imido Derivatives of Titanium(IV) Tetratolylporphyrin

Treatment of (TTP)TiCl2 (1) [TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion] with excess NaOR (R = Ph, Me, t-Bu) affords the bis(alkoxide) derivatives (TTP)Ti(OR)2 [R = Ph (2), Me (3), t-Bu (4)] in moderate yield. The corresponding amido derivative (TTP)Ti(NPh2)2(5) is prepared in an analogous fashion employing LiNPh2. The disubstituted complexes 2, 3, and 5 react cleanly with (TTP)TiCl2 to afford the ligand exchange products (TTP)Ti(OR)Cl [R = Ph (6), Me (7)] and (TTP)Ti(NPh2)Cl (8), respectively. The monosubstituted complexes 6−8are also obtained by treatment of 1 with 1 equiv of the appropriate NaOR or LiNPh2 reagent. Treatment of 5 with excess phenol produces the bis(phenoxide) derivative 2 and 2 equiv of HNPh2. The imido derivatives (TTP)TiNR [R = t-Bu (9), Ph (10), C6H4-p-Me (11)] are prepared by the treatment of 1 with excess LiNHR. The t-Bu derivative (9) is also obtained by reaction of 1 with excess H2N-t-Bu at elevated temperatures. The phenyl imido complex (10) may be produced by the reaction of 0.5 equiv of PhNNPh with (TTP)Ti(η2-EtC⋮CEt) in refluxing toluene. Finally, (TTP)TiNTMS (12) is obtained by oxidation of (TTP)Ti(η2-EtC⋮CEt) with N3TMS

Synthesis, Structure, and Reactivity of Zirconium and Hafnium Imido Metalloporphyrins

The zirconium and hafnium porphyrin imido complexes (TTP)MNAriPr [TTP = meso-tetra-p-tolylporphyrinato dianion, M = Zr (1), Hf (2), AriPr = 2,6-diisopropylphenyl] were synthesized from (TTP)MCl2 and 2 equiv of LiNHAriPr. The zirconium imido complex, (TTP)ZrNAriPr, was also obtained from the preformed imido complex Zr(NAriPr)Cl2(THF)2 and (TTP)Li2(THF)2. Treatment of (TTP)HfCl2 with excess LiNH(p-MeC6H4) resulted in the formation of a bis(amido) complex, (TTP)Hf(NH-p-MeC6H4)2 (3), instead of an imido complex. In the presence of excess aniline, 2 formed an equilibrium mixture of bis(amido) compounds, (TTP)Hf(NHPh)(NHAriPr) and (TTP)Hf(NHPh)2. The nucleophilic character of the imido moiety is exhibited by its reaction with tBuNCO, producing isolable N,O-bound ureato metallacycles. The kinetic product obtained with zirconium, (TTP)Zr(η2-NAriPrC(NtBu)O) (4a), isomerized to (TTP)Zr(η2-NtBuC(NAriPr)O) (4b) in solution. Upon being heated to 80 °C, 4a produced the carbodiimide AriPrNCNtBu and a transient Zr(IV) oxo complex. The analogous hafnium complex (TTP)Hf(η2-NAriPrC(NtBu)O) (5a) did not eject the carbodiimide upon heating to 110 °C but isomerized to (TTP)Hf(η2-NtBuC(NAriPr)O) (5b). To support the formulation of 4a and 5a as N,O bound, the complex (TTP)Hf(η2-NAriPrC(NAriPr)O) (6) was studied by variable-temperature NMR spectroscopy. The corresponding thio- and selenoureato metallacycles were not isolable in the reaction between 1 and 2 with tBuNCS and tBuNCSe. Concomitant formation of the metallacycle with decomposition to the carbodiimide, AriPrNCNtBu, reflects the lower C−Ch bond strength in the proposed N,Ch-bound metallacycles. Treatment of 2 with 1,3-diisopropylcarbodiimide resulted in the η2-guanidino complex (TTP)Hf(η2-NAriPrC(NiPr)NiPr) (7a), which isomerized to the less sterically crowded isomer (TTP)Hf(η2-NiPrC(NAriPr)NiPr) (7b). Complexes 1, 2, 4a, 4b, and7a were characterized by X-ray crystallography. The monomeric terminal imido compounds, 1and 2, are isomorphous:  M−Nimido distances of 1.863(2) Å (Zr) and 1.859(2) Å (Hf); M−Nimido−C angles of 172.5(2)° (Zr) and 173.4(2)° (Hf). The structures of the ureato complexes 4aand 4b and the guanidino complex 7a exhibit typical alkoxido and amido bond distances (Zr−N = 2.1096(13) Å (4a), 2.137(3) Å (4b); Zr−O = 2.0677(12) Å (4a), 2.066(3) Å (4b); Hf−N = 2.087(2) Å, 2.151(2) Å (7a))

Addition and Metathesis Reactions of Zirconium and Hafnium Imido Complexes

The zirconium and hafnium imido metalloporphyrin complexes (TTP)MNAriPr (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; AriPr = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(μ-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of (TTP)ZrNAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (μ-oxo)bis(μ-hydroxo)-bridged dimer [(TTP)Zr]2(μ-O)(μ-OH)2 (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction

Devotions for Lent 2023 Hymns of Lent

This Lent, we will continue reflecting on hymns of faith, namely, some of our most beloved Lenten hymns. 10 such hymns have been chosen to fill the 40(+) days of Lent. Therefore, this devotional, different from previous editions, does not proceed on a weekly basis, but merely flows from one hymn to the next. Also different from previous editions, the devotional reflections are specifically based on the stanzas of the selected hymns. Therefore, each day’s reflection features the text of the hymn stanza, a devotion based on that stanza, a prayer, and then a Scripture passage or passages for further meditation. I pray these reflections may be of edification for you during this Lenten season.https://scholar.csl.edu/osp/1022/thumbnail.jp

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

Group 4 metalloporphyrin alkoxido, amido, hydrazido, and imido complexes: synthesis and reactivity

Previous examinations of group 4 coordination chemistry have predominately involved cyclopentadienyl, alkoxido, and amido complexes. The systematic exploration of the chemistry of group 4 metalloporphyrin complexes has recently been made possible by facile routes to useful porphyrin starting materials. Of interest are complexes containing hard pi-donor ligands. From these, bonding characteristics and steric constraints of the porphyrin periphery specific to the ligand can be studied;The implementation of the group 4 metal halide complexes, (TTP)MCl 2, in metathesis reactions has provided routes to amido, alkoxido, hydrazido, and imido derivatives. These complexes have subsequently demonstrated unique reactivity properties. It has been found that the formation of zirconium and hafnium imido metalloporphyrin complexes is dependent on the steric bulk of the phenyl substituent of the lithiated amide. Bis(amido) complexes are isolable when the ortho positions of phenyl amide are unsubstituted. The presence of the sterically demanding methyl, tert-butyl, or isopropyl groups at the ortho position of the phenyl amide effects an alpha-elimination of a primary aryl amine from the unstable secondary bis(amido) precursor to produce the imido derivative. These imido compounds were key starting materials for the production and investigation of a number of complexes containing M-O bonds. The zirconium and hafnium imido complexes, (TTP)M= NAriPr , couple two pinacolone molecules with concomitant loss of the amine H2 NAriPr . The hydrazido, (TTP)Ti=NNR2 (R = Me, Ph), and imido, (TTP)Ti=NiPr, derivatives of titanium undergo novel nitrene group metathesis reactions with p-chlorobenzaldehyde and with nitrosobenzene, respectively;Additional examples of atom and group transfer involving titanium(II) metalloporphyrins have been demonstrated. Utilization of a variety of donor molecules has facilitated the estimation of the double bond strength for complexes of the type (TTP)Ti=G (G = O, S, Se, NR). This dissertation focuses on the synthesis and reactivity of group 4 metalloporphyrin complexes containing hard pi-donor ligands and on the properties of titanium(II) metalloporphyrin species.</p

Synthesis and Reactivity of Hydrazido(2-) and Imido Derivatives of Titanium(IV) Tetratolylporphyrin

Titanium porphyrin hydrazido complexes (TTP)TiNNR2 (TTP = meso-tetra-p-tolylporphyrinato dianion; R = Me (1), Ph (2)) were synthesized by treatment of (TTP)TiCl2with 1,1-disubstituted hydrazines H2NNR2 (R = Me, Ph) in the presence of piperidine. The nucleophilic character of the hydrazido moiety was demonstrated in the reactions of complexes 1 and 2 with p-chlorobenzaldehyde, which yielded the titanium oxo complex (TTP)TiO and the respective hydrazones. Protonation of complexes 1 and 2 with phenol or water produced the 1,1-disubstituted hydrazine along with (TTP)Ti(OPh)2 or (TTP)TiO, respectively. Similar reactivity of p-chlorobenzaldehyde and phenol with (TTP)TiNiPr, 3, was observed. The reaction of complex 3 with nitrosobenzene cleanly formed the azo compound iPrNNPh and the terminal oxo product (TTP)TiO.Reprinted (adapted) with permission from Inorganic Chemistry 39 (2000): 1301, doi:10.1021/ic990991l. Copyright 2000 American Chemical Society.</p