Synthesis And Characterization Of (9-BBN)di(pyrazoly)borate Complexes

Poly?pyrazolyl?borate is a well known multidentate ligand that can coordinate to a variety of metals to form stable complexes,and widely employed in various fields of chemistry such as coordination,bioinorganic chemistry,catalysis,bionics,materials science and radioactivity.In addition,poly?pyrazolyl?borates are ideal ligands for studying the relationship between structure and reaction of complexes due to the easy control of steric and electronic effects by changing the nature of substituents on the pyrazolyl ring.In this dissertation,six kinds of?9-BBN?bis?pyrazolyl?borate ligands?[?BBN?Bpx]??were synthesized and then reacted with NiCl₂?PPh₃?₃,PdCl₂,cis-PtCl₂?SEt?₂ and MnCl₂ to form twenty two new different complexes,which were fully characterized and most of which contained the agostic or anagostic weak interaction.During the synthesis of these complexes,ligand exchanges were usually accompanied by the cleavage,rearrangement or hydrolysis of B-N bonds.The specific research contents of this dissertation are as follows:Firstly,six kinds of?9-BBN?bis?pyrazolyl?borate ligands M[?BBN?Bp^x]?M=K,Li?were synthesized by the mixture of 9-Borabicyclo[3.3.1]nonane dimer?[{BBN}H]₂,9-BBN dimer?,pyrazole?pz^xH,x=H,Me,ⁱPr,3-Me-4-Br,3,5-Me²,3,5-Me²-4-Br?and metal hydride?KH or LiH?in toluene under reflux and washed with n-hexane.Secondly,thirteen kinds of Ni complexes were obtained by the reaction of the above six ligands and NiCl₂?PPh₃?₃.Among of them,the reaction of ligand[?BBN?BpMe]??2?with NiCl₂?pph?₃ formed two isomers:red planar Ni[BBN?3-Me-pz?2]2?8?and green tetrahedral Ni[BBN?3-Me-pz?2]2?9?,with the latter could transform into the former under certain conditions.Due to the steric hindrance of methyl substituent on the pyrazole ring,the ligand underwent 1,2-borotropic shift to give 9 first at room temperature.When 9 was further heated under reflux in toluene,it underwent the second 1,2-borotropic shift to give 8.If more steric ligand[?BBN?BpiPr]??3?was introduced in the reaction,it led to the B-N bond cleavage and formation of NiCl₂(Bp^ipr)₄?10?,indicating that higher steric substituents on the pyrazole ring prefer ligand rearrangement or B-N bond breakage.If an electron withdrawing Br substituent was further introduced on the pyrazole ring,ie,the ligand[?BBN?Bp^Me,4Br]??4?was reacted with NiCl₂?PPh₃?₃,unexpectedly,ligand rearrangement did not occur at this time.The obtained complex 7 was structurally similar to 9 that they both have tetrahedral Ni centers.However,1,2-borotropic shift was not found in the formation of 7 which may be attributed to the electronic effect of Br.When ligands[?BBN?Bp3,5-Me2]??5?and[?BBN?Bp3,5-Me²-4-Br]??6?were reacted with NiCl₂?PPh₃?₃,complexes Ni[BBN?3,5-Me²-pz?₃BBN?OH?₂]?11?and Ni[BBN?3,5-Me²-4-Br-pz?₃BBN?OH?₂]?12?were obtained by partial hydrolysis of the ligand.In addition,the reaction of 6 with NiCl2?PPh3?3 also produced a binuclear complex Ni₂Cl₂?3,5-Me²-4-Br-pz?[BBN?3,5-Me²-4-Br-pz?₂]₂?13?.It is speculated that the solvent dichloromethane was involved in the reaction,indicating that the solvent effect also affects the formation of complexes.Thirdly,the reaction between ligand 1,2 or 3 and MnCl₂ gave five bis?pyrazolyl?borate manganese complexes Mn[?BBN?Bp]2?19?,Mn[BBN?pz?2]2?pz??20?,Mn[BBN?3-Me-pz?₂]₂?3-Me-pz??21?,Mn[(C₈H₁₄)?O?B?pz?₂]₂?22?and MnCl₂(Bp^ipr)₄?23?,respectively.Among of them,the formation of complex 22 was particularly special.It was supposed that O₂ might participate in the reaction,leading to the B-C bond cleavage of the BBN ring,insertion of an oxygen atom into the B and C atoms to form a C-O-B bond,and further coordination of the O atom to Mn.This O atom insertion reaction is likely a process regulated by Mn due to its oxophilicity.However,this phenomenon was not observed in the reaction of ligand 1 or 2 with MnCl₂.Whether 3 is coordinated with a Mn or a Ni center,the degradation of B-N bond took place.The obtained complexes 23 and 10 are structurally similar.Finally,reactions of ligands 1 and 2 with PdCl₂ and cis-PtCl₂?SEt?₂,respectively,produced complexes Pd[BBN?pz?₂]₂?24?,Pt[?BBN?Bp]₂?25?,Pd[BBN?3-Me-pz?₂]₂?26?and Pt[BBN?3-Me-pz?2]2?27?.Similar to the reaction with Ni,1,2-borotropic shift also occurred during the formation of 26 and 27.In summary,when?9-BBB?bis?pyrazolyl?borate ligands are coordinated to a metal center,the formation of complexes may influenced by steric hindrance and electronic effect of the ligand,solvent effect and even the properties of metals.Due to the rigid structure of BBN rings,most obtained complexes show the intramolucular agostic or anagostic weak interaction.These complexes and their structural features will pave the way for further study of their properties,new design and synthesis of complexes,and application in other fields.