A method for the synthesis of a bi-functional complex comprising a molecule part and an identifier oligonucleotide part identifying the molecule part, said method comprising the steps of i) providing a solid support, ii) providing an optionally protected first identifier oligonucleotide tag comprising a chemical reaction site capable of reacting with a first reactive compound building block and capable of reacting with a further reactive compound building block, iii) providing a first reactive compound building block, wherein the first identifier oligonucleotide tag identifies the first reactive compound building block, iv) covalently linking the first identifier oligonucleotide tag to the solid support, v) reacting in an organic solvent the first reactive compound building block with the chemical reaction site of the first identifier oligonucleotide tag identifying the first reactive compound building block, wherein the first identifier oligonucleotide tag is covalently linked to the solid support when the first reactive compound building block is reacted with the chemical reaction site of the first identifier oligonucleotide tag, wherein the reaction of the first reactive compound building block and the first identifier oligonucleotide tag generates a first intermediate, bi-functional complex comprising a first molecule part and an optionally protected first identifier oligonucleotide tag covalently linked to the solid support, vi) reacting in an organic solvent the first intermediate bi-functional complex obtained in step v) with a second reactive compound building block in the absence of a second identifier oligonucleotide tag identifying the second reactive compound building block, wherein the first intermediate bi-functional complex is covalently linked to the solid support when the second reactive compound building block is reacted with the chemical reaction site and/or reacted with the first molecule part of the first intermediate bi-functional complex, wherein the reaction of the second reactive compound building block and the first intermediate bi-functional complex generates a second intermediate, bi-functional complex covalently linked to the solid support, vii) cleaving the second intermediate bi-functional complex obtained in step vi) from the solid support, and viii) enzymatically ligating in solution the first identifier oligonucleotide tag of said second intermediate bi-functional complex cleaved from said solid support to a second identifier oligonucleotide tag identifying the second reactive compound building block, wherein the enzymatic ligation of the first and second identifier oligonucleotide tags generates a third intermediate bi-functional complex comprising a molecule part and an identifier oligonucleotide part identifying said molecule part. i) providing a solid support, ii) providing an optionally protected first identifier oligonucleotide tag comprising a chemical reaction site capable of reacting with a first reactive compound building block and capable of reacting with a further reactive compound building block, iii) providing a first reactive compound building block, wherein the first identifier oligonucleotide tag identifies the first reactive compound building block, iv) covalently linking the first identifier oligonucleotide tag to the solid support, v) reacting in an organic solvent the first reactive compound building block with the chemical reaction site of the first identifier oligonucleotide tag identifying the first reactive compound building block, wherein the first identifier oligonucleotide tag is covalently linked to the solid support when the first reactive compound building block is reacted with the chemical reaction site of the first identifier oligonucleotide tag, wherein the reaction of the first reactive compound building block and the first identifier oligonucleotide tag generates a first intermediate, bi-functional complex comprising a first molecule part and an optionally protected first identifier oligonucleotide tag covalently linked to the solid support, vi) reacting in an organic solvent the first intermediate bi-functional complex obtained in step v) with a second reactive compound building block in the absence of a second identifier oligonucleotide tag identifying the second reactive compound building block, wherein the first intermediate bi-functional complex is covalently linked to the solid support when the second reactive compound building block is reacted with the chemical reaction site and/or reacted with the first molecule part of the first intermediate bi-functional complex, wherein the reaction of the second reactive compound building block and the first intermediate bi-functional complex generates a second intermediate, bi-functional complex covalently linked to the solid support, vii) cleaving the second intermediate bi-functional complex obtained in step vi) from the solid support, and viii) enzymatically ligating in solution the first identifier oligonucleotide tag of said second intermediate bi-functional complex cleaved from said solid support to a second identifier oligonucleotide tag identifying the second reactive compound building block, wherein the enzymatic ligation of the first and second identifier oligonucleotide tags generates a third intermediate bi-functional complex comprising a molecule part and an identifier oligonucleotide part identifying said molecule part.