1 research outputs found
Amido Ca and Yb(II) Complexes Coordinated by Amidine-Amidopyridinate Ligands for Catalytic Intermolecular Olefin Hydrophosphination
A series
of amido Ca and YbÂ(II) complexes LMÂ[NÂ(SiMe<sub>3</sub>)<sub>2</sub>]Â(THF) (<b>1Yb</b>, <b>1–4Ca</b>) coordinated
by amidine-amidopyridinate ligands <b>L</b><sup><b>1</b>–<b>4</b></sup> were synthesized via a transamination
reaction between proligands <b>L</b><sup><b>1</b>–<b>4</b></sup><b>H</b> and bisamido complexes MÂ[NÂ(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>Â(THF)<sub>2</sub> (M = Yb,
Ca). The reactions of YbÂ[NÂ(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>Â(THF)<sub>2</sub> with proligands <b>L</b><sup><b>2</b></sup><b>H</b>-<b>L</b><sup><b>4</b></sup><b>H</b> containing CF<sub>3</sub> and C<sub>6</sub>H<sub>4</sub>F fragments do not allow for preparing the target YbÂ(II) complexes,
while the Ca analogues were synthesized in good yields. Complexes <b>1Yb</b> and <b>1</b>–<b>4Ca</b> were evaluated
as precatalysts for hydrophosphination of styrene, <i>p</i>-substituted styrenes, α-Me-styrene, and 2,3-dimethylbutadiene
with various primary and secondary phosphines (PhPH<sub>2</sub>, 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>PH<sub>2</sub>, 2-C<sub>5</sub>NH<sub>4</sub>PH<sub>2</sub>, Ph<sub>2</sub>PH, Cy<sub>2</sub>PH). Complexes <b>1Yb</b>, <b>1</b>–<b>4Ca</b> performed high
catalytic activities in styrene hydrophosphination with PhPH<sub>2</sub> and Ph<sub>2</sub>PH and demonstrated high regioselectivity affording
exclusively the anti-Markovnikov addition products. For primary PhPH<sub>2</sub> the reactions (1:1 molar ratio of substrates) catalyzed by <b>1Yb</b>, <b>1Ca</b>, and <b>2Ca</b> proved to be highly
chemoselective affording the secondary phosphine PhÂ(PhCH<sub>2</sub>CH<sub>2</sub>)ÂPH; however, complexes <b>3Ca</b> and <b>4Ca</b> led to the formation of both secondary and tertiary phosphines
in 80:20 and 86:14 ratios. Styrene hydrophosphinations with 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>PH<sub>2</sub> and 2-pyridylphosphine
for all complexes <b>1Yb</b> and <b>1–4Ca</b> proceeded
much more slowly compared to PhPH<sub>2</sub>. Addition of 2-C<sub>5</sub>NH<sub>4</sub>PH<sub>2</sub> to styrene catalyzed by complex <b>1Yb</b> 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 <b>1Ca</b> and <b>1Yb</b> 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 Cy<sub>2</sub>PH, 2-C<sub>5</sub>NH<sub>4</sub>PH<sub>2</sub>, and PhPH<sub>2</sub>, but less active with sterically demanding 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>PH<sub>2</sub>. Styrenes containing in <i>p</i>-position electron-donating groups (Me, tBu, OMe) performed
with noticeably lower rates in the reactions with PhPH<sub>2</sub> compared to styrene. Complexes <b>1Yb</b>, <b>1Ca</b>, <b>2Ca</b>, <b>3Ca</b>, and <b>4Ca</b> enabled
addition of PhPH<sub>2</sub> toward the double Cî—»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 <b>1Ca</b> and <b>2Ca</b> promoted 1,2-addition
of PhPH<sub>2</sub> to 2,3-dimethyl butadiene with excellent regio-
and chemoselectivity to afford linear secondary phosphines. Hydrophosphination
of inert 1-nonene with Ph<sub>2</sub>PH with 40% conversion becomes
possible due to the application of complex <b>2Ca</b> (40 h,
70 °C). The rate law for the hydrophosphination of styrene with
Ph<sub>2</sub>PH catalyzed by <b>1Ca</b> was found to agree
with the idealized equation: <i>v</i> = <i>k</i>[styrene]<sup>1</sup>[<b>1Ca</b>]<sup>1</sup>