An FYI, the Lewis acid is HgI2 (from the same class below, which gave the same article that philmont found).
I suppose I should clarify, I'm not saying that OSiR3 will not chelate metals. I'm saying bulky silyl groups have been shown to not chelate metals nearly as well as less sterically encumbered groups. A benzyl group would be much better for chelation than a silyl group (excluding maybe TMS, etc.) TIPS, TBS, and TBDPS decrease in chelate selectivity with size, this is from: JACS 1992, 114, 1778 using Me2Mg as a Lewis acid. I imagine it varies with Lewis acid as well.
The above article also discusses kinetic evidence for chelation and silyl groups certainly slow down the reaction... five member-ed chelates (alpha) are faster than 6 member-ed chelates (beta), etc. Also, beta chelation is not as strong as alpha chelation, so without proper choice of solvents, it can be hard to obtain good selectivity.