About

Lawrence R. Sita is a professor in the Department of Chemistry and Biochemistry at the University of Maryland, with a research focus on transition and main group metal inorganic and organometallic chemistry. His work involves the discovery, development, and implementation of molecular catalysts and atom-economical catalytic transformations aimed at producing commodity chemicals and advanced materials while reducing environmental impact and human health concerns. His research seeks to elucidate the fundamental principles governing the structure and bonding of transition-metal complexes, and to apply this knowledge to design highly efficient catalysts for industrial feedstocks. Additionally, his group develops new polymeric materials through a material science and engineering approach, contributing to advanced technological applications.

Research topics

• Polymer chemistry
• Photochemistry
• Organic chemistry
• Chemistry

Selected publications

• Monomer Discrimination in the Enantioselective Living Coordinative Chain Transfer Polymerization of α,ω-Nonconjugated Dienes vs α-Olefins

  ACS Catalysis · 2025-03-13 · 4 citations

  articleSenior authorCorresponding

  The stereoselective living coordinative polymerization (LCP) of α-olefins and α,ω-nonconjugated dienes can be achieved using initiators derived from the homochiral, configurationally stable, monocyclopentadienyl, 7- and 9-membered-ring cycloamidinate group 4 metal complexes, 1–3, respectively, as preinitiators in combination with borate B1 as activating co-initiator. However, yield, molar mass (Mn), and degree of stereoregularity in these LCPs were found to be highly dependent upon initial monomer concentration due to decreased magnitudes for monomer complexation and site isomerization, KM, and KSI, respectively. The enantioselective living coordinative chain transfer polymerization (LCCTP) of 1,5-hexadiene using the initiator derived from 1/B1 and excess equivalents of ZnEt2 as chain transfer agent (CTA) provides isotactic cis/trans poly(methylene-1,3-cyclopentane) (PMCP) in high yield. In contrast, under identical conditions, all attempts to carry out the enantioselective LCCTP of 1-hexene failed. It is proposed that this unprecedented discrimination of polymerizability between the two monomer types for LCCTP is due to stark differences in conformational freedom of the growing polyolefin chains. More specifically, in the case of the rigid-rod nature of growing PMCP, reversible chain transfer is not sterically impeded and can occur as required, whereas the unrestricted conformational flexibility of side chains in poly(1-hexene) creates a steric barrier that prohibits chain transfer to occur after just a few monomer insertions. Collectively, these results provide insights for designs of the next generation of enantiopure and configurationally stable cycloamidinate preinitiators that can potentially lead to the successful enantioselective LCCTP of both α,ω-nonconjugated dienes and α-olefins with high stereoregularity.

  PublisherDOI

• A Living Telomerization Process for the Versatile and Scalable Production of ω-Substituted Fatty Alcohols and Acids

  ACS Catalysis · 2025-07-15 · 3 citations

  articleSenior authorCorresponding

  Transition-metal-mediated living ternary chain transfer telomerization (LTCTT) of a wide variety of tris(ω-substituted alkyl)aluminum telogens, [X-(CH2)mCH2CH2]3Al (7), which can be obtained in abundant quantities from commodity chemicals through an atom-economical process that generates no chemical waste, is reported that utilizes inexpensive ethene to produce isomerically pure (>97%) ω-substituted fatty alcohols, X-(CH2)m(CH2CH2)n-1CH2CH2OH (IV), after a reactive quench with O2, and the corresponding ω-substituted fatty acids, X-(CH2)m(CH2CH2)n-1CH2CO2H (V), via subsequent oxidation, where m = 0 and 1 are for even- and odd-carbon-numbered series, respectively. The Poisson distribution of n-mers of IV and V can either be used ‘as is’ or fractionated into separate n-mer components, some of which cannot be easily obtained by any other synthetic means. Preliminary validation of LTCTT includes the selective syntheses of odd- and even-carbon-numbered branched chain fatty acids (BCFAs) of the iso-1 (X = iso-butyl) and anteiso-2 (X = sec-butyl) series, which are known to be beneficial for human health but currently lack a natural or synthetic source that can provide large secure quantities. Other successful demonstrations of LTCTT being reported include (1) production of the aryl-terminated fatty acids 3 (X = phenyl) and 4 (X = p-fluorophenyl), which are important building blocks for the synthesis of pharmacologically active compounds, (2) the cyclohexyl terminated fatty acids 5 (X = Cy), which are key lipid components of thermophiles, and (3) the series of (ω-y)-Et-main chain branched fatty acids 6a (y = 7) and 6b (y = 9) that represent an unexplored class of ‘lipoid’ precursors for lipid nanoparticles. The potential of both trialkyl aluminum telogens and LTCTT to provide practical and scalable quantities of a wide structural range of different classes of IV and V now opens the door for scientific, technological, and health-related advances.

  PublisherDOI

• Sterically Reduced Cyclopentadienyl, Amidinate Group 4 Metal Initiators for Living Coordination Chain-Transfer Polymerization with Challenging Metals and Monomers

  Macromolecules · 2025-12-15

  articleSenior authorCorresponding

  Reduction of nonbonded steric interactions within the supporting cyclopentadienyl, amidinate (CPAM) ligand environment of group 4 metal dimethyl complexes of general formula, (η5-C5R5)[κ2-(N,N)-N(R1)C(R2)N(R3)]MMe2 (I), render these capable of serving as initiators for the living coordination polymerization (LCP) and living coordinative chain-transfer polymerization (LCCTP) of challenging alkene monomers, such as vinylcyclohexene (VCH). More specifically, the active ion pair initiator derived from the Cs-symmetric Hf preinitiator 1 (M = Hf; R = R1 = R3; R2 = Ph) and the anilinium borate co-initiator, [PhNHMe2][B(C6F5)4] (B1), provides isotactic poly(vinylcyclohexane) (iPVCH) through LCP via a chain-end stereocontrol mechanism, and in the presence of 5 equiv of diethylzinc (ZnEt2) as a chain-transfer agent, the LCCTP of VCH provides end-group-functionalized atactic PVCH using a reactive quench with I2. Finally, the active initiator obtained from the CPAM Ti preinitiator 2 (M = Ti; R = H, R1 = R3 = Me, R2 = Ph) and either B1, [Ph3C][B(C6F5)4] (B2), or B(C6F5)3 (B3) as a co-initiator, was shown to be competent for the nonliving coordination polymerizations of ethene, propene, and 1-hexene.

  PublisherDOI

• Understanding the Thin Film Confinement Impact on the Glass Transition and Dynamic Fragility of Unentangled Atactic, <i>Cis</i> Poly(Methylene‐1,3‐Cyclohexane)

  Journal of Polymer Science · 2025-05-19 · 2 citations

  articleCorresponding

  ABSTRACT Understanding the influences of thin film confinement on supported films, which are reflected in changes of glass transition temperature ( T g ) and dynamic fragility, is important as they can inform the implementation of polymers in nanotechnology. Here, two molecular weights (MWs) of atactic, cis poly(methylene‐1,3‐cyclohexane) (PMCH), 5.5 kDa (PMCH‐5.5) and 12.1 kDa (PMCH‐12.1), were studied to elucidate how their key physical properties are impacted under nanoconfinement. We note both polymers are below the critical MW ( M c ) as confirmed by rheological measurement. Specifically, the MW of unentangled PMCH has a large effect on both the bulk and confinement behaviors of the polymers, where PMCH‐5.5 had a lower T g and was less fragile than PMCH‐12.1. It was also found that decreasing the MW of PMCH could suppress confinement effects. These results not only elucidate the impact of nanoconfinement on the properties of PMCH, compared to other well‐studied polymers including polystyrene, but also can inform their use for emerging applications.

  PublisherDOI

• Stereoselective Living Coordination and Chain Transfer Polymerization of Kempe’s 4-Ethyl-1-alkenes

  Macromolecules · 2025-12-05 · 1 citations

  articleSenior authorCorresponding

  A toolbox of living coordination polymerization (LCP) processes mediated by cyclopentadienyl, amidinate (CPAM) group 4 metal ion pair initiators has been used to convert a family of branched 4-ethyl-1-alkenes, which are now readily accessible in practical quantities through Kempe’s titanium-mediated bis-homologation of linear 1-alkenes with ethene, into isotactic and atactic (iso-rich) forms of the corresponding poly(4-ethyl-1-alkene)s (P4E1As). Application of living coordinative chain transfer polymerization (LCCTP) of these same monomers, in which diethylzinc is employed as a reversible chain transfer agent, further permitted production of scalable quantities of ultralow-molar-mass, end-group-functionalized P4E1As of narrow dispersity (Đ ≤ 1.15) and with targeted DPn values of only 12–13. These highly branched x-P4E1As are of interest as a potential class of “globular” hydrophobic domain building blocks.

  PublisherDOI

• Stereoblock vs Stereoblend: Orchestrating Competing Living Coordination Chain Transfer Polymerizations for the One-Pot Production of New Viscoelastic Grades of Poly(4-methyl-1-pentene)

  ACS Catalysis · 2024-01-30 · 10 citations

  articleSenior authorCorresponding

  By exerting control over two populations of coexisting cyclopentadienyl, amidinate (CPAM) group 4 metal active species that possess different stereoselectivities for chain growth propagation during the living coordinative chain transfer polymerization (LCCTP) of 4-methyl-1-pentene, controlled production of grades for poly(4-methyl-1-pentene) (PMP) materials that display a tunable range of viscoelastic properties can be achieved in “one-pot” fashion. Analytical and spectroscopic investigations reveal that these differences in viscoelastic properties are associated with formation of atactic/isotactic PMP stereoblends, rather than a stereoblock chain architecture. These results serve to establish the ability of low molar mass atactic PMP to function as an effective property modifier for commercially important isotactic PMP, which in its pure form is highly brittle with low tensile strength. The further outcome of these studies is extension of multistate LCCTP as a tool for expanding the range of accessible grades and properties of polyolefins that can be produced from the limited small set of industrially significant olefins.

  PublisherDOI

• Cyclopentadienyl Amidinate Ligand Directing Effects in the Enantioselective Living Coordinative Chain Transfer Polymerization of 1,5-Hexadiene

  Catalysts · 2024-12-20 · 2 citations

  articleOpen accessSenior authorCorresponding

  The new chiral and configurationally stable cyclopentadienyl amidinate (CPAM) hafnium complexes, (RC, RHf)-2 and (SC, SHf)-3, have been obtained in enantio- and diastereomerically pure form. Upon activation with the borate co-initiator, [PhNHMe2][B(C6F5)4] (B1), 2 and 3 can serve as pre-initiators for the enantioselective living coordinative polymerization (LCP) and living coordinative chain transfer polymerization (LCCTP) of 1,5-hexadiene to provide optically active poly (methylene-1,3-cyclopentane) (PMCP) and end-group-functionalized PMCP (x-PMCP) in scalable quantities, respectively. 13C NMR stereochemical microstructural analyses reveal the role of ligand directing effects for the two-step propagation mechanism of 1,2-migratory insertion/ring-closing cyclization and structure/property relationships for these new PMCP and x-PMCP materials.

  PublisherOA PDFDOI

• Rapid Phase Transitions of Thermotropic Glycolipid Quasicrystal and Frank‐Kasper Mesophases: A Mechanistic Rosetta Stone

  Angewandte Chemie International Edition · 2023-04-05 · 20 citations

  articleOpen accessSenior authorCorresponding

  Experimental results are presented that serve to lower the barrier for developing the science and technology of non-classical thermotropic glycolipid mesophases, which now include dodecagonal quasicrystal (DDQC) and Frank-Kasper (FK) A15 and σ mesophases that can be produced under mild conditions from a versatile class of sugar-polyolefin conjugates. By employing "alloys" comprised of mono- and disaccharide-polyolefin conjugates, and optionally with vitamin E as a small molecule phase modulator, we report the spontaneous formation of stable A15 mesophases at ambient temperature. We further document a rich thermotropic phase map that includes DDQC, A15, and σ mesophases of tunable periodicity that are connected through rapid thermotropic phase transitions as a function of increasing temperature in the order: liquid-like packing (LLP)→DDQC → A15→σ→ disorder. This first direct observation of a rapid thermotropic A15→σ phase transition provides support for a diffusionless martensitic process proceeding through strain-induced introduction of planar defects into the A15 lattice.

  PublisherOA PDFDOI

• Rapid Phase Transitions of Thermotropic Glycolipid Quasicrystal and Frank‐Kasper Mesophases: A Mechanistic Rosetta Stone

  Angewandte Chemie · 2023-04-05 · 1 citations

  articleOpen accessSenior authorCorresponding

  Abstract Experimental results are presented that serve to lower the barrier for developing the science and technology of non‐classical thermotropic glycolipid mesophases, which now include dodecagonal quasicrystal (DDQC) and Frank–Kasper (FK) A15 and σ mesophases that can be produced under mild conditions from a versatile class of sugar‐polyolefin conjugates. By employing “alloys” comprised of mono‐ and disaccharide‐polyolefin conjugates, and optionally with vitamin E as a small molecule phase modulator, we report the spontaneous formation of stable A15 mesophases at ambient temperature. We further document a rich thermotropic phase map that includes DDQC, A15, and σ mesophases of tunable periodicity that are connected through rapid thermotropic phase transitions as a function of increasing temperature in the order: liquid‐like packing (LLP)→DDQC → A15→σ→ disorder. This first direct observation of a rapid thermotropic A15→σ phase transition provides support for a diffusionless martensitic process proceeding through strain‐induced introduction of planar defects into the A15 lattice.

  PublisherOA PDFDOI

• Tailoring Glass Transition Temperature in a Series of Poly(methylene-1,3-cyclopentane-<i>stat</i>-cyclohexane) Statistical Copolymers

  ACS Macro Letters · 2023-01-04 · 10 citations

  articleSenior authorCorresponding

  A systematic investigation of the synthesis and characterization of a new class of amorphous atactic cis, trans poly(methylene-1,3-cyclopentane-stat-cyclohexane) statistical copolymers (I) is reported. Production of different grades of I that vary with respect to the ratio of 5- and 6-membered cycloalkane repeat units was achieved through the living coordinative chain transfer cyclopolymerization of different initial feed ratios of 1,5-hexadiene and 1,6-heptadiene comonomers. It was determined that the glass transition temperature, Tg, of I can be systematically increased from −16 to 100 °C as a function of increasing 6-membered ring content, although not in a strictly linear fashion. It was further determined that a small level of 6-membered ring content is sufficient to disrupt the crystallinity of the limiting atactic cis, trans poly(methylene-1,3-cyclopentane) (PMCP) homopolymer that possesses a melting temperature, Tm, of 98 °C. These results establish a foundation for future potential technological applications of this unique class of polyolefin copolymers.

  PublisherDOI

Recent grants

• Dynamic Multi-state Living Coordination Polymerization for Next Generation Polyolefins

  NSF · $600k · 2023–2026

• Catalytic Metal-Mediated Small Molecule Fixation

  NSF · $517k · 2014–2017

• Mechanistic Investigations of Olefin Polymerizations and Selective Oligomerizations

  NSF · $489k · 2009–2012

• Electrocatalytic Metal-Mediated Nitrogen Fixation

  NSF · $450k · 2017–2020

• CAS: New Catalytic Processes for Polyolefin Sustainability and Waste Utilization

  NSF · $490k · 2020–2023

Frequent coauthors

• Peter Y. Zavalij

  University of Maryland, College Park

  116 shared

• Brendan L. Yonke

  58 shared

• Wesley S. Farrell

  United States Naval Academy

  48 shared

• James C. Fettinger

  University of California, Davis

  37 shared

• Andy J. Keane

  33 shared

• Jonathan P. Reeds

  30 shared

• Arnold L. Rheingold

  University of California, San Diego

  27 shared

• R.J. Keaton

  Dow Chemical (United States)

  25 shared

Labs

• Lawrence R. Sita LabPI

Education

• Ph.D. , Chemistry

  Massachusetts Institute of Technology

  1985

• B.S. (Honors), Chemistry

  Carnegie Mellon University

  1981

Awards & honors

• Beckman Young Investigator (1995–1998)
• Camille Dreyfus Teacher-Scholar (1995-2000)
• Faculty Research Award, College of Chemical and Life Science…
• NSF Special Creativity Award (2004–2006)