Photoinduced Regioselective Olefination of Arenes at Proximal and Distal Sites.

The Fujiwara-Moritani reaction has had a profound contribution in the emergence of contemporary C-H activation protocols. Despite the applicability of the traditional approach in different fields, the associated reactivity and regioselectivity issues had rendered it redundant. The revival of this exemplary reaction requires the development of a mechanistic paradigm that would have simultaneous control on both the reactivity and regioselectivity. Often, the high thermal energy required to promote olefination leads to multiple site functionalizations. To this aim, we established a photoredox catalytic system constituting a merger of palladium/organo-photocatalyst (PC) that forges oxidative olefination in an explicit regioselective fashion with diverse arenes and heteroarenes. Visible light plays a significant role in executing "regioresolved" Fujiwara-Moritani reactions without the requirement of silver salts and thermal energy. The catalytic system is also amenable toward proximal and distal olefination aided by the respective directing groups (DGs), which entails the versatility of the protocol in engaging the entire spectrum of C(sp2)-H olefination. Furthermore, streamlining the synthesis of natural products, chiral molecules, drugs, and diversification through late-stage functionalizations underscore the importance of this sustainable protocol. The photoinduced attainment of this regioselective transformation is mechanistically established through control reactions and kinetic studies.

Coligand modulated oxidative O-demethylation of a methyl ether appended tetradentate N-ligand in Co(ii) complexes.

Two Co(ii) complexes of the formula CoLOMeX2 (X = Cl- (1a); X = I- (1b)), where LOMe is 2-methoxy-N,N-bis(pyridin-2-ylmethyl) aniline, were synthesized and their structure, spectra and reactivity were studied. Upon oxidation of 1a and 1b, the ligand LOMe undergoes demethylation at the metal centre resulting in the formation of Co(iii) complexes with modified phenoxide ligands. This is the very first example of oxidative O-demethylation reported at a Co(ii) centre. The oxidative behaviour exhibits a striking dependence on the nature of coligands coordinated to the metal centre. The Co(ii) complex 1a with stronger chloro coligands requires a strong oxidising agent like t-BuOOH for oxidative demethylation and the subsequent formation of a mononuclear Co(iii) complex with a demethylated ligand, CoLO-Cl2 (2). On the other hand, complex 1b with weaker iodo coligands undergoes oxidation in the presence of the weak oxidant O2 to form a dihydroxo bridged binuclear Co(iii) complex [Co2(LO-)2(OH)2]2+ (3) with modified phenoxide ligands. The oxidation of 1b to 3 is monitored and the intermediate Co(ii) iodo aqua complex [CoLOMeI(H2O)]+ and Co(ii) diaqua complex [CoLOMe(H2O)2]2+ are isolated and characterised.

Ligand-Enabled PdII -Catalyzed Iterative γ-C(sp3)-H Arylation of Free Aliphatic Acid.

C-H functionalization of aliphatic carboxylic acids without attaching exogenous auxiliary has been so far limited at the proximal ß-position. In this work, we demonstrate a ligand enabled palladium catalyzed first regioselective distal γ-C(sp3)-H functionalization of aliphatic carboxylic acids without incorporating an exogenous directing group. Aryl iodides containing versatile functional groups including complex organic molecules are well tolerated with good to excellent yields during the γ-C(sp3)-H arylation reaction. Interestingly, weak coordination of carboxylate group can be further extended for sequential hetero di-arylation. Application of the protocol has been showcased by synthesizing substituted α-tetralone. Mechanistic investigations have been carried out to shed light on the reaction pathway.

Iterative Arylation of Amino Acids and Aliphatic Amines via δ-C(sp3 )-H Activation: Experimental and Computational Exploration.

Directed C-H functionalization has been realized as a complementary tool to the traditional approaches for a straightforward access of non-proteinogenic amino acids; albeit such a process is restricted mostly up to the γ-position. In the present work, we demonstrate the diverse (hetero)arylation of amino acids and analogous aliphatic amines selectively at the remote δ-position by tuning the reactivity controlled by ligands. An organopalladium δ-C(sp3 )-H activated intermediate has been isolated and crystallographically characterized. Mechanistic investigations carried out experimentally in conjunction with computational studies shed light on the difference in the mechanistic picture depending on the substrate structure.

Dinuclear cobalt(II) complexes with double phosphate ester bridges and tetradentate ligands having anisole or quinoline appendages.

Phosphate esters provide a rigid and stable polymeric backbone in nucleic acids. Metal complexes with phosphate ester groups have been synthesized as structural and spectroscopic models of phosphate-containing enzymes. Dinucleating ligands are used extensively to synthesize model complexes since they provide the support required to stabilize such complexes. The crystal structures of two dinuclear CoII complexes, namely bis(µ-diphenyl phosphato-κ2O:O')bis({2-methoxy-N,N-bis[(pyridin-2-yl)methyl]aniline-κ4N,N',N'',O}cobalt(II)) bis(perchlorate), [Co(C12H10O4P)2(C19H19N3O)2](ClO4)2, and bis(µ-diphenyl phosphato-κ2O:O')bis({N,N-bis[(pyridin-2-yl)methyl]quinolin-8-amine-κ4N,N',N'',O}cobalt(II)) bis(perchlorate), [Co(C12H10O4P)2(C21H18N4)2](ClO4)2, with tetradentate 2-methoxy-N,N-bis[(pyridin-2-yl)methyl]aniline (L1) and N,N-bis[(pyridin-2-yl)methyl]quinolin-8-amine (L2) ligands are reported. The complexes have similar structures, with distorted octahedral geometries around the metal centres. Both are centrosymmetric (Z' = 0.5), with the CoII centres doubly bridged by diphenyl phosphate ester groups. A number of aromatic-aromatic interactions are present and differ between the two complexes as the anisole group in L1 is replaced by a quinoline group in L2. A detailed study of these interactions is presented.