Samir H. Chikkali

Long-Chain Polyacetals From Plant Oils

Plant oil-derived α,ω-diacetals are polycondensated to the novel polyacetals [OCH(2) O(CH(2))(y)](n) (y = 19 and 23) with molecular weight of ca. M(n) = 2 × 10(4) g mol(-1). The long methylene sequences provide substantial melt and crystallization temperatures (T(m) = 88 °C and T(c) = 68 °C for y = 23), and rates of hydrolytic degradation are dramatically lower for the long-chain polyacetals versus a shorter chain analogue (y = 12) studied for comparison.

Sustainable polyacetals from isohexides

A single step synthetic protocol to access a small family of renewable diacetals was established. The resultant chiral diacetals are valuable building blocks in pharmaceuticals and materials science. To demonstrate their synthetic competence, isohexide-diacetals (2a–c) were subjected to acetal metathesis polymerization and the corresponding polymers (poly2a–c) were isolated as white solids with molecular weights in the range 3200–27600 (g mol−1). The semi-crystalline polymers displayed glass transition temperatures between 38–65 °C and melting temperatures in the range 103–156 °C. The isohexide derived polyacetals are stable under practical washing and rinsing conditions but degrade in slightly acidic media.

Highly Regioselective Isomerizing Hydroformylation of Long-Chain Internal Olefins Catalyzed by a Rhodium Bis(Phosphite) Complex

The single‐step synthesis, coordination behavior, and application of a bis(phosphite) ligand in the isomerizing hydroformylation of internal olefins was investigated. Interestingly, high‐pressure NMR spectroscopy investigations revealed unexpected inequivalency of the two phosphorus nuclei, which display bisequatorial coordination of the bis(phosphite) ligand in a trigonal bipyramidal rhodium complex. Upon employment in the isomerizing hydroformylation of the exceedingly challenging plant oil derived substrate methyl oleate, the bis(phosphite) rhodium complex revealed an unprecedented linear selectivity of 75 %.

The impact of modular substitution on crystal packing: the tale of two ureas

A small library of 13 (3a–m) compounds with modular positioning of iodide and urea/thiourea groups was synthesized in excellent yields in a single step synthetic protocol. The existence of the anticipated (thio)urea derivatives was unambiguously established using a combination of 1–2D NMR spectroscopy, ESI-MS and single crystal X-ray diffraction studies. These (thio)urea compounds were classified into four classes as follows: a) mono-substituted urea, b) di-substituted urea, c) di-substituted thiourea and d) electronically tailored di-substituted thiourea. The changes in molecular conformation and crystal packing due to the change in the relative positioning of the iodo group at the phenyl ring attached to one of the N atoms and different substituents at other N atoms in urea and thiourea derivatives have been discussed. The urea derivatives, in general, display the chain association through one-dimensional three-centered N–H⋯O hydrogen bonding interactions due to the trans–trans orientation of both NH protons with respect to the carbonyl group, whereas the thiourea compounds exhibit a centrosymmetric dimeric assembly via the complementary N–H⋯S interactions because of the trans–cis arrangement of the NH protons leading to either a helical or a sheet pattern. The presence of a nitro group at the para position of the thiourea derivative leads to trans–trans arrangement of both NH protons with respect to the thiocarbonyl groups, thus yielding a chain assembly through one-dimensional three-centered N–H⋯S interactions similar to urea derivatives. Associations of these chains or sheets in urea/thiourea derivatives through halogen bonding interactions (hal⋯hal, hal⋯π, hal⋯S etc.) generate a 2D assembly.

Isomerizing Hydroformylation of Cashew Nut Shell Liquid

A small library of bisphosphorus ligands was evaluated in the rhodium‐catalyzed isomerizing hydroformylation (I‐HF) of cashew nut shell liquid (CNSL). The rhodium complex of 1,2‐bis((di‐tert‐butylphosphanyl)methyl)benzene (BDTBPMB; L4) outperformed the other bisphosphite and bisphosphine ligands and unveiled a moderate selectivity of 28 % and 50 % in the I‐HF of CNSL monoene and methoxy‐protected monoene, respectively. The resultant aldehyde 16‐(3‐methoxyphenyl)hexadecanal P1′ was isolated and its identity was fully established. Application of bis‐phosphine ligand L4 in the I‐HF of highly challenging CNSL cardanol (S3) and methoxy‐protected CNSL cardanol yielded a linear selectivity of 74 %, although with reduced conversion. To demonstrate the synthetic utility of our strategy, the obtained aldehyde (derived from S3) was subjected to hydrogenation and the resultant 3‐(16‐hydroxyhexadecyl) phenol (P8) was isolated in 89 % isolated yield. High‐pressure NMR investigation revealed selective formation of a bis‐equatorial BDTBPMB–rhodium complex, which might be responsible for the excellent linear selectivity.

Secondary Interactions Arrest the Hemiaminal Intermediate To Invert the Modus Operandi of Schiff Base Reaction: A Route to Benzoxazinones

Discovered by Hugo Schiff, condensation between amine and aldehyde represents one of the most ubiquitous reactions in chemistry. This classical reaction is widely used to manufacture pharmaceuticals and fine chemicals. However, the rapid and reversible formation of Schiff base prohibits formation of alternative products, of which benzoxazinones are an important class. Therefore, manipulating the reactivity of two partners to invert the course of this reaction is an elusive target. Presented here is a synthetic strategy that regulates the sequence of Schiff base reaction via weak secondary interactions. Guided by the computational models, reaction between 2,3,4,5,6-pentafluoro-benzaldehyde with 2-amino-6-methylbenzoic acid revealed quantitative (99%) formation of 5-methyl-2-(perfluorophenyl)-1,2-dihydro-4H-benzo[d][1,3]oxazin-4-one (15). Electron donating and electron withdrawing ortho-substituents on 2-aminobenzoic acid resulted in the production of benzoxazinones 9-36. The mode of action was tracked using low temperature NMR, UV-vis spectroscopy, and isotopic (18O) labeling experiments. These spectroscopic mechanistic investigations revealed that the hemiaminal intermediate is arrested by the hydrogen-bonding motif to yield benzoxazinone. Thus, the mechanistic investigations and DFT calculations categorically rule out the possibility of in situ imine formation followed by ring-closing, but support instead hydrogen-bond assisted ring-closing to prodrugs. This unprecedented reaction represents an interesting and competitive alternative to metal catalyzed and classical methods of preparing benzoxazinone.

Iron Catalyzed Hydroformylation of Alkenes under Mild Conditions: Evidence of an Fe(II) Catalyzed Process

Earth abundant, first row transition metals offer a cheap and sustainable alternative to the rare and precious metals. However, utilization of first row metals in catalysis requires harsh reaction conditions, suffers from limited activity, and fails to tolerate functional groups. Reported here is a highly efficient iron catalyzed hydroformylation of alkenes under mild conditions. This protocol operates at 10-30 bar syngas pressure below 100 °C, utilizes readily available ligands, and applies to an array of olefins. Thus, the iron precursor [HFe(CO)4]-[Ph3PNPPh3]+ (1) in the presence of triphenyl phosphine catalyzes the hydroformylation of 1-hexene (S2), 1-octene (S1), 1-decene (S3), 1-dodecene (S4), 1-octadecene (S5), trimethoxy(vinyl)silane (S6), trimethyl(vinyl)silane (S7), cardanol (S8), 2,3-dihydrofuran (S9), allyl malonic acid (S10), styrene (S11), 4-methylstyrene (S12), 4- iBu-styrene (S13), 4- tBu-styrene (S14), 4-methoxy styrene (S15), 4-acetoxy styrene (S16), 4-bromo styrene (S17), 4-chloro styrene (S18), 4-vinylbenzonitrile (S19), 4-vinylbenzoic acid (S20), and allyl benzene (S21) to corresponding aldehydes in good to excellent yields. Both electron donating and electron withdrawing substituents could be tolerated and excellent conversions were obtained for S11-S20. Remarkably, the addition of 1 mol % acetic acid promotes the reaction to completion within 16-24 h. Detailed mechanistic investigations revealed in situ formation of an iron-dihydride complex [H2Fe(CO)2(PPh3)2] (A) as an active catalytic species. This finding was further supported by cyclic voltammetry investigations and intermediacy of an Fe(0)-Fe(II) species was established. Combined experimental and computational investigations support the existence of an iron-dihydride as the catalyst resting state, which then follows a Fe(II) based catalytic cycle to produce aldehyde.

Modern trends in inorganic chemistry: celebration of inorganic chemistry in India

Which is the most exciting research topic in “Inorganic Chemistry” being pursued in India? This question may have multiple debatable responses, but the most likely event which would offer an answer would be the gathering of practising inorganic chemists of the country, in the Modern Trends in Inorganic Chemistry (MTIC). Briefly,Modern Trends in Inorganic Chemistry is a series of biennial symposia that was initiated in 1985 at the Indian Association for the Cultivation of Science, Kolkata, India. Ever since its inception, MTIC has been an important forum for the inorganic chemists of the country and remains the most sought-after event to showcase their science. CSIR-NCL in associationwith IISERPune and SP Pune University had the pleasure of hosting the 17th edition of MTIC in Pune during 11−14th Dec. 2017. After brief remarks by the convener Dr. Amitava Das, MTIC-XVII opened with two inaugural talks by two eminent inorganic chemists, namely, Prof. Animesh Chakravorty and Dr. T. Ramasami. Prof. Chakravorty, a founder member of MTIC, shared his academic and research experience titled “An old man’s album of inorganic chemistry”, aptly suited for a person of his stature, while Dr. Ramasami emphasized on how inorganic chemistry can be best utilized to address the need of our countrymen. A talk titled “Joy of doing useful inorganic chemistry” was delivered by Dr. T. Ramasami, a champion and stalwart in a public-private research partnership with enormous experience in research and science policy. These two talks set the perfect stage for the remaining proceedings. Eminent academicians, as well as representatives from the industry presented and discussed the latest and most exciting aspects of structural, inorganic, organometallic, spectroscopic and computational chemistry. MTIC-XVII provided a vital forum for the exchange of new ideas amongst the active inorganic chemists in a constructive and interdisciplinary atmosphere and offered a common platform to strengthen the international network of inorganic and organometallic chemists of this country. The symposium featured a blend of ten distinguished international speakers, and close to seventy active Indian researchers covering industry, academia and research institutions. Most importantly, around 500 research students/scholars who are pursuing their Ph.D. participated actively in this symposium and presented over 350 posters. MTIC-XVII was, in its own spirit, an effort to bring together all the stakeholders to foresee the future of inorganic chemistry in the country and to make our lives better. Selected papers presented during the symposiumwere considered for bringing out a Special Issue onMTIC-XVII. Based on the presentations showcased, contributions were invited and after peer review, 26 papers have been accepted for publication in the Journal of Chemical Sciences as a Special Issue. This special issue comprises of review articles, perspectives, communications and full-length articles. As you will witness, the special issue features contemporary science of immense importance and showcases the rich heritage of inorganic chemistry in India. The organizers of MTIC-XVII thank the Editorial Board of the Journal of Chemical Sciences and Indian Academy of Sciences, Bengaluru, for accepting our proposal to bring out a special issueonMTIC-XVII.Wewould like to take this opportunity to thank the Editor-in-Chief, Prof. N. Periasamy, for guidance to publish this special issue.We profoundly appreciate and thank the authors who have contributed to this special issue. The process would not have been complete without the stringent peer review; we thank the reviewers for enabling the review process. We are obliged to the editorial staff of Journal of Chemical Sciences and the publishing and production team of Springer Nature for their assistance at various levels during the publication and production of this special issue.

H-Bonding Assisted Self-Assembly of Anionic and Neutral Ligand on Metal: A Comprehensive Strategy To Mimic Ditopic Ligands in Olefin Polymerization

Self-assembly of two neutral ligands on a metal to mimic bidentate ligand coordination has been frequently encountered in the recent past, but self-assembly of an anionic ligand on a metal template alongside a neutral ligand remains an elusive target. Such a self-assembly is hampered by additional complexity, wherein a highly negatively charged anion can form intermolecular hydrogen bonding with the supramolecular motif, leaving no scope for self-assembly with neutral ligand. Presented here is the self-association of anionic ligand 3-ureidobenzoic acid (2a) and neutral ligand 1-(3-(diphenylphosphanyl)phenyl)urea (1a) on a metal template to yield metal complex [{COOC6H4NH(CO)NH2}{Ph2PC6H4NH(CO)NH2}PdMeDMSO] (4a). The identity of 4a was established by NMR and mass spectroscopy. Along the same lines, 3-(3-phenylureido)benzoic acid (2b) and 1-(3-(diphenylphosphanyl)phenyl)-3-phenylurea (1b) self-assemble on a metal template to produce palladium complex [{COOC6H4NH(CO)NHPh}{Ph2PC6H4NH(CO)NHPh}PdMePy] (5c). The existence of 5c was confirmed by Job plot, 1-2D NMR spectroscopy, deuterium labeling, IR spectroscopy, UV-vis spectroscopy, model complex synthesis, and DFT calculations. These solution and gas phase investigations authenticated the presence of intramolecular hydrogen bonding between hydrogens of 1b and carbonyl oxygen of 2b. The generality of the supramolecular approach has been validated by preparing six complexes from four monodentate ligands, and their synthetic utility was demonstrated in ethylene polymerization. Complex 4a was found to be the most active, leading to the production of highly branched polyethylene with a molecular weight of 55700 g/mol and melting temperature of 112 °C.