Safrole (4-allyl-1,2-methylendioxybenzene) is obtained from oil extracted from sassafras, an evergre — Inorganic Chemistry Chemistry Question
Safrole
Safrole (4-allyl-1,2-methylendioxybenzene) is obtained from oil extracted from sassafras, an evergreen tree growing in the central and northern regions of Vietnam. Safrole has interesting functionality and chemical reactivity suggesting its use as an efficient and versatile natural synthon in the synthesis of numerous biologically active compounds. [PtCl(Safrole-1H)(Pyridine)] is a complex with a similar activity to the anticancer drug Cisplatin. [PtCl(Safrole-1H)(Pyridine)] has been synthesized for the first time by chemists at the Department of Chemistry, Hanoi National University of Education. The reaction scheme is given below.
[VISUAL]
Some spectral signals of uncoordinated safrole and coordinated safrole in A, B and C are given below.
[VISUAL]
Write balanced equations for the three reactions in the above scheme.
Model Answer
Reaction 1: K[PtCl3C2H4] + C10H10O2 → K[PtCl3(C10H10O2)] + C2H4
Reaction 2: 2 K[PtCl3(C10H10O2)] → [Pt2Cl2(C10H9O2)2] + 2 KCl + 2 HCl
Reaction 3: [Pt2Cl2(C10H9O2)2] + 2 C5H5N → 2 [PtCl(C10H9O2)(C5H5N)]
What information about the coordination of safrole with Pt in A, B and C can be obtained from the IR and 1H NMR data?
Model Answer
- In A:
- From IR data: C9 and C10 bond with Pt
- From 1H NMR data: safrole coordinated with Pt
- In B:
- From IR data: C9 and C10 bond with Pt
- From 1H NMR data: safrole lost H5, C5 bonds with Pt
- In C:
- From IR data: C9 and C10 bond with Pt
- From 1H NMR data: safrole lost H5, C5 bonds with Pt
Draw the structures of A, B and C, given that in C pyridine is in the cis-position with respect to the allyl group of safrole.
Model Answer
The coordinates and structures are described as:
- Complex A: K[PtCl3(Safrole)] where safrole is coordinated mono-dentately through its allylic C9=C10 double bond to the Pt atom.
- Complex B: [Pt2Cl2(Safrole-1H)2] which is a dimeric complex. Each safrole ligand is bidentate, coordinating through both the C9=C10 double bond and a Pt-C5 sigma bond, with two bridging chloride ligands.
- Complex C: [PtCl(Safrole-1H)(Pyridine)] where the dimer is cleaved by pyridine, which coordinates to Pt in the position cis to the allylic double bond of safrole.
What is the driving force of each of the reactions (1), (2) and (3)?
Model Answer
- Reaction 1: Ethylene (C2H4) is a volatile gas that escapes from the reaction mixture, shifting the equilibrium in favor of complex A.
- Reaction 2: The formation of the chelate complex [Pt2Cl2(C10H9O2)2] provides extra stability (chelate effect).
- Reaction 3: Pyridine (C5H5N) is a strong nucleophile and ligand that forms a stronger Pt-N bond than the bridging Pt-Cl bonds in the dimer.
Why does reaction 3 not seem to obey the trans effect?
Model Answer
This reaction is controlled by steric effects rather than the trans effect.