Pyrazolyl-pyrimidine porous-organic-polymer supported single-site nickel composites as efficient catalysts for the synthesis of substituted pyrimidines

•A novel porous organic polymer-supported single-site nickel catalyst has been synthesized.•Single-site catalyst exhibits excellent catalytic activity in the one-pot synthesis of poly-substituted pyrimidine derivatives.•The reaction mechanism of acceptorless dehydrogenation of oximes and alcohols was detailed investigated.•The prepared catalyst could be recovered and reused for at least eight times.