52-Hydroxy/(benzyloxy)-3,5-ditertbutyl benzaldehyde reacts with PhSeCH 2 CH 2 NH 2 resulting in sterically hindered selenoether ligand (Schiff base) [2−HO−3,5−(C(CH 3 ) 3 ) 2 −C 6 H 2 −C=N−(CH 2 ) 2 SePh] (L1)/ [2−PhCH 2 O−3,5−(C(CH 3 ) 3 ) 2 −C 6 H 2 −CH 2 −NH−(CH 2 ) 2 SePh] (L2). The reactions of L1 and L2 with Na 2 PdCl 4 in methanol and acetone-water mixture at room temperature have resulted in complexes, [PdCl (L1-H)] (1) and [PdCl 2 (L2)] (2)], respectively. Both the complexes and their ligands have been 10 characterized with 1 H, 13 C{ 1 H} and 77 Se{ 1 H} NMR spectroscopy. The molecular structures of complexes 1 and 2 have been determined with single crystal X-ray diffraction. The Pd−Se bond lengths in 1 and 2 are 2.370(1) and 2.366(1) Å, respectively. The geometry around palladium in both the complexes is nearly square planar. Complexes 1 and 2 (0.1 mol % Pd) have been found efficient as catalyst for Suzuki-Miyaura C−C coupling reactions in the presence of K 2 CO 3 in ethanol. The catalysis in water with 15 complex 1 in the presence of K 2 CO 3 was found feasible but with low conversion (up to 40%). The efficiency of 1 in carrying out the coupling is marginally better than that of 2. 65 range of substrates and many functional groups are tolerated due to mild reaction conditions. This is very helpful in the total synthesis of complex molecules including drugs. (ii) Phenylboronic acid, starting material is readily available, stable and sustainable. 15 (iii) The product biaryl is a very important core 70 component of various biologically and pharmaceutically important compounds (viz. anti-hypertensive, anti-cancer, antibiotic, anti-inflammatory, and antifungal) and in nonlinear optical materials. 16 75

The condensation of 2-(phenylsulfanyl)­ethylamine and 2-(phenylselenyl)­ethylamine with anthracene-9-carbaldehyde resulted in Schiff bases [PhS­(CH2)2CN-9-C14H9]­(L1) and [PhSe­(CH2)2CN-9-C14H9] (L2), respectively. Na2[PdCl4] treatment of L1/L2 in acetone–water mixture for 3 h at room temperature gave palladacycle [PdCl­(C–, N, S/Se)] (1/2; L1/L2–H = (C–, N, S)/(C–, N, Se)). The reaction of [(η6-C6H6)­RuCl­(μ-Cl)]2 with L1/L2 in methanol for 8 h at room temperature (followed by addition of NH4PF6) afforded half-sandwich complex [(η6-C6H6)­Ru­(L)­Cl]­[PF6], 3/4: (L = L1/L2 ≡ (N, E) ligand). The reaction of [(η5-Cp*)­RhCl­(μ-Cl)]2 with L1 /L2 in the presence of CH3COONa at 50 °C (followed by treatment with NH4PF6) resulted in [(η5-Cp*)­Rh­(L-H)]­[PF6], 5/6: (L = L1/L2). On carrying out the reaction of [(η5-Cp*)­RhCl­(μ-Cl)]2 with these ligands at room temperature and in the absence of CH3COONa, complex [(η5-Cp*)­Rh­(L)­Cl]­[PF6], 7/8 (L = L1/L2 ≡ (N, E) ligand), was formed. Complexes 1–8 were authenticated with 1H, 13C­{1H}, and 77Se­{1H} NMR spectroscopy, high-resolution mass spectrometry, elemental analyses, and single-crystal X-ray diffraction. The moisture- and air-insensitive complexes of Pd­(II) (1, 2), Ru­(II) (3, 4) and Rh­(III) (5–8) were thermally stable. Palladium and rhodium (under base-free condition) species efficiently catalyzed transfer hydrogenation (propan-2-ol as H-source). At room temperature conversion was 90% in TH catalyzed with 0.2 mol % of 2. N-Alkylation of aniline with benzyl alcohol under base-free condition was promoted by 3–8. The 7 was most efficient for the two base-free catalytic reactions. For TH optimum loading of 1–2 and 5–8 as catalyst is 0.05–0.2 and 0.2–0.5 mol % respectively. The optimum temperatures are 80 and 100 °C for TH and N-alkylation, respectively. The optimum loading of 3–8 for N-alkylation is 0.5 mol %. Mercury poisoning test supported homogeneous pathway for the two catalytic reactions. The rhodacycles probably gave real catalytic species by losing a Cp* group.

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The condensation of anthracene-9-carbaldehyde with 2-(phenylthio/seleno)ethylamine results in Schiff bases [PhS(CH)C[double bond, length as m-dash]N-9-CH](L1) and [PhSe(CH)C[double bond, length as m-dash]N-9-CH] (L2). On their reaction with [(η-Cp*)IrCl(μ-Cl)] and CHCOONa at 50 °C followed by treatment with NHPF, iridacycles, [(η-Cp*)Ir(L-H)][PF] (1: L = L1; 2: L = L2), result. The same reaction in the absence of CHCOONa gives complexes [(η-Cp*)Ir(L)Cl][PF] (3-4) in which L = L1(3)/L2(4) ligates in a bidentate mode. The ligands and complexes were authenticated with HR-MS and NMR spectra [H, C{H} and Se{H} (in the case of L2 and its complexes only)]. Single crystal structures of L2 and half sandwich complexes 1-4 were established with X-ray crystallography. Three coordination sites of Ir in each complex are covered with η-Cp* and on the remaining three, donor atoms present are: N, S/Se and C/Cl, resulting in a piano-stool structure. The moisture and air insensitive 1-4 act as efficient catalysts under mild conditions for base free N-alkylation of amines with benzyl alcohols and transfer hydrogenation (TH) of aldehydes/ketones. The optimum loading of 1-4 as a catalyst is 0.1-0.5 mol% for both the activations. The best reaction temperature is 80 °C for transfer hydrogenation and 100 °C for N-alkylation. The mercury poisoning test supports a homogeneous pathway for both the reactions catalyzed by 1-4. The two catalytic processes are most efficient with 3 followed by 4 > 1 > 2. The mechanism proposed on the basis of HR-MS of the reaction mixtures of the two catalytic processes taken after 1-2 h involves the formation of an alkoxy and hydrido species. The real catalytic species proposed in the case of iridacycles results due to the loss of the Cp* ring.