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

Tricarbonyl(chlorodiphenylstannyl){η5-[2-(dimethylamino)ethyl]cyclopenta­dienyl}molybdenum

Reaction of the tricarbon­yl{η5-[2-(dimethyl­amino)eth­yl]cyclo­penta­dien­yl}molybdenum anion and dichlorido­diphenyl­stannane affords the title compound, [MoSn(C6H5)2Cl(C9H14N)(CO)3], which exhibits a four-legged piano-stool geometry with chlorido­diphenyl­stannyl ligands unperturbed by the pendant 2-(dimethyl­amino)ethyl groups. The Mo—Sn bond length [2.7584 (5) Å] and the distortion of the tetra­hedral tin coordination geometry are similar to those observed in related tin-substituted tricarbonyl­molybdenum and -tungsten complexes

Making Connections - Envisioning Springfield\u27s North End

This work explores a service learning strategy in the context of the senior Urban Design Studio taught in the Department of Landscape Architecture and Regional Planning at the University of Massachusetts Amherst. The primary goal of this project is to stimulate a conversation in the neighborhoods of the North End, to develop green design strategies, to improve services and businesses for residents and the employees of local businesses, and to foster cultural engagement and interaction in the North End that will enhance the vibrancy, resilience, and quality of life of this urban community. Making connections - Envisioning Springfield\u27s North End proposes improved connectivity in a physical, cultural, and social sense will be key to attaining these goals and to engaging and synergizing individuals and community groups in the North End - residents, businesses, schools, churches, employers, and employees. Six sustainable learning and planning principles have emerged from this studio: 1. Input and interaction – Visioning workshops connect campus and community 2. Community-building art - Expression of place and people 3. Healthy living - Urban agriculture and education 4. Urban greenways – Abandoned railways and urban rivers and streams 5. Green infrastructure - Green streets as networks and structural framework 6. Sustainable urban form – Mixed use and pedestrian friendly neighborhood