In the March/April 2019 edition of Taxation of Exempts, Christopher Moran published "Giving Retirement Assets to a Charitable Remainder Trust." Here is a summary of the article.
"If retirement plan assets are left to a CRT for the life of the surviving spouse, the spouse will get an income stream for life, without the income tax drawbacks associated with leaving plan assets to a QTIP trust. No action will be required of the surviving spouse, the spouse will not be able to withdraw the benefits in a lump sum, the participant can choose the ultimate charitable beneficiary, and, if the spouse is the only noncharitable beneficiary, the retirement assets will be shielded from estate tax at the participant's death and the surviving spouse's death. Thus, if the participant does not want to leave retirement plan assets outright to the surviving spouse, using the plan assets to fund a CRT for the surviving spouse is an excellent alternative to leaving such assets to a QTIP trust."