Amido Ca and Yb(II) Complexes Coordinated by Amidine-Amidopyridinate Ligands for Catalytic Intermolecular Olefin Hydrophosphination.

A series of amido Ca and Yb(II) complexes LMN(SiMe) (1Yb, 1-4Ca) coordinated by amidine-amidopyridinate ligands L were synthesized via a transamination reaction between proligands LH and bisamido complexes MN(SiMe) (M = Yb, Ca). The reactions of YbN(SiMe) with proligands LH-LH containing CF and CHF fragments do not allow for preparing the target Yb(II) complexes, while the Ca analogues were synthesized in good yields. Complexes 1Yb and 1-4Ca were evaluated as precatalysts for hydrophosphination of styrene, p-substituted styrenes, α-Me-styrene, and 2,3-dimethylbutadiene with various primary and secondary phosphines (PhPH, 2,4,6-MeCHPH, 2-CNHPH, PhPH, CyPH). Complexes 1Yb, 1-4Ca performed high catalytic activities in styrene hydrophosphination with PhPH and PhPH and demonstrated high regioselectivity affording exclusively the anti-Markovnikov addition products. For primary PhPH the reactions (1:1 molar ratio of substrates) catalyzed by 1Yb, 1Ca, and 2Ca proved to be highly chemoselective affording the secondary phosphine Ph(PhCHCH)PH; however, complexes 3Ca and 4Ca led to the formation of both secondary and tertiary phosphines in 80:20 and 86:14 ratios. Styrene hydrophosphinations with 2,4,6-MeCHPH and 2-pyridylphosphine for all complexes 1Yb and 1-4Ca proceeded much more slowly compared to PhPH. Addition of 2-CNHPH to styrene catalyzed by complex 1Yb turned out to be non-regioselective and led to the formation of a mixture of Markovnikov and anti-Markovnikov addition products, while all Ca complexes enabled regioselective anti-Markovnikov addition. Complexes 1Ca and 1Yb containing catalytic centers featuring similar ionic radii performed different catalytic activity: the ytterbium analogue proved to be a more active catalyst for intermolecular hydrophosphination of styrene with CyPH, 2-CNHPH, and PhPH, but less active with sterically demanding 2,4,6-MeCHPH. Styrenes containing in p-position electron-donating groups (Me, tBu, OMe) performed with noticeably lower rates in the reactions with PhPH compared to styrene. Complexes 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca enabled addition of PhPH toward the double C═C bond of α-Me-styrene, and the reaction rate for this substrate is noticeably lower; however quantitative conversions were reached in ∼40 h. Complexes 1Ca and 2Ca promoted 1,2-addition of PhPH to 2,3-dimethyl butadiene with excellent regio- and chemoselectivity to afford linear secondary phosphines. Hydrophosphination of inert 1-nonene with PhPH with 40% conversion becomes possible due to the application of complex 2Ca (40 h, 70 °C). The rate law for the hydrophosphination of styrene with PhPH catalyzed by 1Ca was found to agree with the idealized equation: v = k[styrene][1Ca].